Add GN output prefix override and allow empty output extensions.

tools/gn/docs/reference.md

 # GN Reference
 
 *This page is automatically generated from* `gn help --markdown all`.
 
 ## **\--args**: Specifies build arguments overrides.
 
 ```
   See "gn help buildargs" for an overview of how build arguments work.
 
   Most operations take a build directory. The build arguments are taken
@@ skipping 2827 matching lines @@
 
     output_prefix  [string]
         Valid for: Linker tools (optional)
 
         Prefix to use for the output name. Defaults to empty. This
         prefix will be prepended to the name of the target (or the
         output_name if one is manually specified for it) if the prefix
         is not already there. The result will show up in the
         {{output_name}} substitution pattern.
 
+        Individual targets can opt-out of the output prefix by setting:
+          output_prefix_override = true
+        (see "gn help output_prefix_override").
+
         This is typically used to prepend "lib" to libraries on
         Posix systems:
           output_prefix = "lib"
 
     precompiled_header_type  [string]
         Valid for: "cc", "cxx", "objc", "objcxx"
 
         Type of precompiled headers. If undefined or the empty string,
         precompiled headers will not be used for this tool. Otherwise
         use "gcc" or "msvc".
@@ skipping 1799 matching lines @@
 
 ```
 ## **output_extension**: Value to use for the output's file extension.
 
 ```
   Normally the file extension for a target is based on the target
   type and the operating system, but in rare cases you will need to
   override the name (for example to use "libfreetype.so.6" instead
   of libfreetype.so on Linux).
 
-  This value should not include a leading dot. If undefined or empty,
-  the default_output_extension specified on the tool will be used.
-  The output_extension will be used in the "{{output_extension}}"
+  This value should not include a leading dot. If undefined, the default
+  specified on the tool will be used. If set to the empty string, no
+  output extension will be used.
+
+  The output_extension will be used to set the "{{output_extension}}"
   expansion which the linker tool will generally use to specify the
   output file name. See "gn help tool".
 
 ```
 
 ### **Example**
 
 ```
   shared_library("freetype") {
     if (is_linux) {
@@ skipping 37 matching lines @@
 
 ### **Example**
 
 ```
   static_library("doom_melon") {
     output_name = "fluffy_bunny"
   }
 
 
 ```
+## **output_prefix_override**: Don't use prefix for output name.
+
+```
+  A boolean that overrides the output prefix for a target. Defaults to
+  false.
+
+  Some systems use prefixes for the names of the final target output
+  file. The normal example is "libfoo.so" on Linux for a target
+  named "foo".
+
+  The output prefix for a given target type is specified on the linker
+  tool (see "gn help tool"). Sometimes this prefix is undesired.
+
+  See also "gn help output_extension".
+
+```
+
+### **Example**
+
+```
+  shared_library("doom_melon") {
+    # Normally this will produce "libdoom_melon.so" on Linux, setting
+    # Setting this flag will produce "doom_melon.so".
+    output_prefix_override = true
+    ...
+  }
+
+
+```
 ## **outputs**: Output files for actions and copy targets.
 
 ```
   Outputs is valid for "copy", "action", and "action_foreach"
   target types and indicates the resulting files. Outputs must always
   refer to files in the build directory.
 
   copy
     Copy targets should have exactly one entry in the outputs list. If
     there is exactly one source, this can be a literal file name or a
@@ skipping 387 matching lines @@
 
   Just these specific targets:
     visibility = [ ":mything", "//foo:something_else" ]
 
   Any target in the current directory and any subdirectory thereof, plus
   any targets in "//bar/" and any subdirectory thereof.
     visibility = [ "./*", "//bar/*" ]
 
 
 ```
+## **write_runtime_deps**: Writes the target's runtime_deps to the given path.
+
+```
+  Does not synchronously write the file, but rather schedules it
+  to be written at the end of generation.
+
+  If the file exists and the contents are identical to that being
+  written, the file will not be updated. This will prevent unnecessary
+  rebuilds of targets that depend on this file.
+
+  Path must be within the output directory.
+
+  See "gn help runtime_deps" for how the runtime dependencies are
+  computed.
+
+  The format of this file will list one file per line with no escaping.
+  The files will be relative to the root_build_dir. The first line of
+  the file will be the main output file of the target itself. The file
+  contents will be the same as requesting the runtime deps be written on
+  the command line (see "gn help --runtime-deps-list-file").
+
+
+```
 ## **Build Arguments Overview**
 
 ```
   Build arguments are variables passed in from outside of the build
   that build files can query to determine how the build works.
 
 ```
 
 ### **How build arguments are set**
 
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   works and advice on fixing problems. Targets can also opt-out of
   checking, see "gn help check_includes".
 
 
 ```
 ## **Runtime dependencies**
 
 ```
   Runtime dependencies of a target are exposed via the "runtime_deps"
   category of "gn desc" (see "gn help desc") or they can be written
-  at build generation time via "--runtime-deps-list-file"
-  (see "gn help --runtime-deps-list-file").
+  at build generation time via write_runtime_deps(), or
+  --runtime-deps-list-file (see "gn help --runtime-deps-list-file").
 
   To a first approximation, the runtime dependencies of a target are
   the set of "data" files, data directories, and the shared libraries
   from all transitive dependencies. Executables, shared libraries, and
   loadable modules are considered runtime dependencies of themselves.
 
 ```
 
 ### **Executables**
 
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 **  -q**: Quiet mode. Don't print output on success.
 **  \--root**: Explicitly specify source root.
 **  \--runtime-deps-list-file**: Save runtime dependencies for targets in file.
 **  \--threads**: Specify number of worker threads.
 **  \--time**: Outputs a summary of how long everything took.
 **  \--tracelog**: Writes a Chrome-compatible trace log to the given file.
 **  -v**: Verbose logging.
 **  \--version**: Prints the GN version number and exits.
 
 ```