[Mac/GN] Set up the component build.

build/toolchain/mac/BUILD.gn

Index: build/toolchain/mac/BUILD.gn
diff --git a/build/toolchain/mac/BUILD.gn b/build/toolchain/mac/BUILD.gn
index 571865c7fd3b277b578bca7e153e3315959c659f..931f6657fb214e233caaabd38d30b92482f98186 100644
--- a/build/toolchain/mac/BUILD.gn
+++ b/build/toolchain/mac/BUILD.gn
@@ -138,12 +138,11 @@ template("mac_toolchain") {
 
       does_reexport_command = "[ ! -e \"$dylib\" -o ! -e \"$tocname\" ] || otool -l \"$dylib\" | grep -q LC_REEXPORT_DYLIB"
 
-      link_command =
-          "$ld -shared {{ldflags}} -o \"$dylib\" -Wl,-filelist,\"$rspfile\""
+      link_command = "$ld -shared "

[Robert Sesek, 2016/05/06 19:17:36]

This is the hack I mentioned in the standup:

GN doesn't have any concept of install name vs output name, nor can you
filter/check set ldflags. This is an issue with bundled dylib targets, where the
install name differs from the output name, and the install name has to be set by
the target itself. The solution here places the generic
is_component_build-generated install name flag ahead of ldflags, so that if the
target specifies the install name in ldflags, the latter one on the command line
takes precedence.

       if (is_component_build) {
-        link_command += " -Wl,-install_name,@rpath/{{target_output_name}}{{output_extension}}"
+        link_command += " -Wl,-install_name,@rpath/\"{{target_output_name}}{{output_extension}}\" "
       }
-      link_command += " {{solibs}} {{libs}}"
+      link_command += "{{ldflags}} -o \"$dylib\" -Wl,-filelist,\"$rspfile\" {{libs}} {{solibs}}"
 
       replace_command = "if ! cmp -s \"$temporary_tocname\" \"$tocname\"; then mv \"$temporary_tocname\" \"$tocname\""
       extract_toc_command = "{ otool -l \"$dylib\" | grep LC_ID_DYLIB -A 5; nm -gP \"$dylib\" | cut -f1-2 -d' ' | grep -v U\$\$; true; }"