Enable cross compile to android from mac.

build/toolchain/gcc_toolchain.gni

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This value will be inherited in the toolchain below.
 concurrent_links = exec_script("get_concurrent_links.py", [], "value")
 
 # This template defines a toolchain for something that works like gcc
 # (including clang).
 #
 # It requires the following variables specifying the executables to run:
 #  - cc
 #  - cxx
 #  - ar
 #  - ld
+#  - readelf
+#  - nm
 # and the following which is used in the toolchain_args
 #  - toolchain_cpu  (What "current_cpu" should be set to when invoking a
 #                    build using this toolchain.)
 #  - toolchain_os  (What "current_os" should be set to when invoking a
 #                   build using this toolchain.)
 #
 # Optional parameters:
 #  - libs_section_prefix
 #  - libs_section_postfix
 #      The contents of these strings, if specified, will be placed around
 #      the libs section of the linker line. It allows one to inject libraries
 #      at the beginning and end for all targets in a toolchain.
 #  - solink_libs_section_prefix
 #  - solink_libs_section_postfix
 #      Same as libs_section_{pre,post}fix except used for solink instead of link.
 #  - post_solink
 #      The content of this string, if specified, will be appended to the solink
 #      command.
 #  - deps
 #      Just forwarded to the toolchain definition.
 #  - is_clang
 template("gcc_toolchain") {
   toolchain(target_name) {
     assert(defined(invoker.cc), "gcc_toolchain() must specify a \"cc\" value")
     assert(defined(invoker.cxx), "gcc_toolchain() must specify a \"cxx\" value")
     assert(defined(invoker.ar), "gcc_toolchain() must specify a \"ar\" value")
     assert(defined(invoker.ld), "gcc_toolchain() must specify a \"ld\" value")
+    assert(defined(invoker.readelf),
+           "gcc_toolchain() must specify a \"readelf\" value")
+    assert(defined(invoker.nm), "gcc_toolchain() must specify a \"nm\" value")
     assert(defined(invoker.toolchain_cpu),
            "gcc_toolchain() must specify a \"toolchain_cpu\"")
     assert(defined(invoker.toolchain_os),
            "gcc_toolchain() must specify a \"toolchain_os\"")
 
     # We can't do string interpolation ($ in strings) on things with dots in
     # them. To allow us to use $cc below, for example, we create copies of
     # these values in our scope.
     cc = invoker.cc
     cxx = invoker.cxx
     ar = invoker.ar
     ld = invoker.ld
+    readelf = invoker.readelf
+    nm = invoker.nm
 
     # Bring these into our scope for string interpolation with default values.
     if (defined(invoker.libs_section_prefix)) {
       libs_section_prefix = invoker.libs_section_prefix
     } else {
       libs_section_prefix = ""
     }
 
     if (defined(invoker.libs_section_postfix)) {
       libs_section_postfix = invoker.libs_section_postfix
@@ skipping 66 matching lines @@
       rspfile = sofile + ".rsp"
 
       # These variables are not built into GN but are helpers that implement
       # (1) linking to produce a .so, (2) extracting the symbols from that file
       # to a temporary file, (3) if the temporary file has differences from the
       # existing .TOC file, overwrite it, otherwise, don't change it.
       tocfile = sofile + ".TOC"
       temporary_tocname = sofile + ".tmp"
       link_command =
           "$ld -shared {{ldflags}} -o $sofile -Wl,-soname=$soname @$rspfile"
-      toc_command = "{ readelf -d $sofile | grep SONAME ; nm -gD -f p $sofile | cut -f1-2 -d' '; } > $temporary_tocname"
+      toc_command = "{ $readelf -d $sofile | grep SONAME ; $nm -gD -f p $sofile | cut -f1-2 -d' '; } > $temporary_tocname"
       replace_command = "if ! cmp -s $temporary_tocname $tocfile; then mv $temporary_tocname $tocfile; fi"
 
       command = "$link_command && $toc_command && $replace_command"
       if (defined(invoker.postsolink)) {
         command += " && " + invoker.postsolink
       }
       rspfile_content = "-Wl,--whole-archive {{inputs}} {{solibs}} -Wl,--no-whole-archive $solink_libs_section_prefix {{libs}} $solink_libs_section_postfix"
 
       description = "SOLINK $sofile"
 
@@ skipping 62 matching lines @@
       if (defined(invoker.is_clang)) {
         is_clang = invoker.is_clang
       }
     }
 
     if (defined(invoker.deps)) {
       deps = invoker.deps
     }
   }
 }