Make GN Android build link executables

build/toolchain/gcc_toolchain.gni

Index: build/toolchain/gcc_toolchain.gni
diff --git a/build/toolchain/gcc_toolchain.gni b/build/toolchain/gcc_toolchain.gni
index 9e53ef667e049ae8334475373de738342b5df3ad..91baa11b8473190d519cc501fb01378a5a5a6147 100644
--- a/build/toolchain/gcc_toolchain.gni
+++ b/build/toolchain/gcc_toolchain.gni
@@ -14,6 +14,13 @@
 #                         build using this toolchain.)
 #  - toolchain_os  (What "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.
 template("gcc_toolchain") {
   toolchain(target_name) {
     assert(defined(invoker.cc), "gcc_toolchain() must specify a \"cc\" value")
@@ -33,6 +40,19 @@ template("gcc_toolchain") {
     ar = invoker.ar
     ld = invoker.ld
 
+    # 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
+    } else {
+      libs_section_postfix = ""
+    }
+
     # Make these apply to all tools below.
     lib_prefix = "-l"
     lib_dir_prefix="-L"
@@ -56,13 +76,13 @@ template("gcc_toolchain") {
       description = "AR \$out"
     }
     tool("solink") {
-      command = "if [ ! -e \$lib -o ! -e \${lib}.TOC ]; then $ld -shared \$ldflags -o \$lib -Wl,-soname=\$soname -Wl,--whole-archive \$in \$solibs -Wl,--no-whole-archive \$libs && { readelf -d \${lib} | grep SONAME ; nm -gD -f p \${lib} | cut -f1-2 -d' '; } > \${lib}.TOC; else $ld -shared \$ldflags -o \$lib -Wl,-soname=\$soname -Wl,--whole-archive \$in \$solibs -Wl,--no-whole-archive \$libs && { readelf -d \${lib} | grep SONAME ; nm -gD -f p \${lib} | cut -f1-2 -d' '; } > \${lib}.tmp && if ! cmp -s \${lib}.tmp \${lib}.TOC; then mv \${lib}.tmp \${lib}.TOC ; fi; fi"
+      command = "if [ ! -e \$lib -o ! -e \${lib}.TOC ]; then $ld -shared \$ldflags -o \$lib -Wl,-soname=\$soname -Wl,--whole-archive \$in \$solibs -Wl,--no-whole-archive \$libs && { readelf -d \${lib} | grep SONAME ; nm -gD -f p \${lib} | cut -f1-2 -d' '; } > \${lib}.TOC; else $ld -shared \$ldflags -o \$lib -Wl,-soname=\$soname -Wl,--whole-archive \$in \$solibs -Wl,--no-whole-archive $libs_section_prefix \$libs $libs_section_postfix && { readelf -d \${lib} | grep SONAME ; nm -gD -f p \${lib} | cut -f1-2 -d' '; } > \${lib}.tmp && if ! cmp -s \${lib}.tmp \${lib}.TOC; then mv \${lib}.tmp \${lib}.TOC ; fi; fi"
       description = "SOLINK \$lib"
       #pool = "link_pool"
       restat = "1"
     }
     tool("link") {
-      command = "$ld \$ldflags -o \$out -Wl,--start-group \$in \$solibs -Wl,--end-group \$libs"
+      command = "$ld \$ldflags -o \$out -Wl,--start-group \$in \$solibs -Wl,--end-group $libs_section_prefix \$libs $libs_section_postfix"
       description = "LINK \$out"
       #pool = "link_pool"
     }