GN build fixes, mostly for Mac.

tools/gn/gyp_binary_target_writer.cc

Index: tools/gn/gyp_binary_target_writer.cc
diff --git a/tools/gn/gyp_binary_target_writer.cc b/tools/gn/gyp_binary_target_writer.cc
index e32c60bff5a5a05deaeeb6de89e00e9f4143c1c9..cb6b4e01b5ba33d3dfd3bd503663b08c81af8daa 100644
--- a/tools/gn/gyp_binary_target_writer.cc
+++ b/tools/gn/gyp_binary_target_writer.cc
@@ -7,6 +7,7 @@
 #include <set>
 
 #include "base/logging.h"
+#include "base/strings/string_util.h"
 #include "tools/gn/builder_record.h"
 #include "tools/gn/config_values_extractors.h"
 #include "tools/gn/err.h"
@@ -66,6 +67,32 @@ std::string GetVCOptimization(std::vector<std::string>* cflags) {
   return "'2'";  // Default value.
 }
 
+// Returns the value from the already-filled in cflags for the processor
+// architecture to set in the GYP file. Additionally, this removes the flag
+// from the given vector so we don't get duplicates.
+std::string GetMacArch(std::vector<std::string>* cflags) {
+  // Searches for the "-arch" option and returns the corresponding GYP value.
+  for (size_t i = 0; i < cflags->size(); i++) {
+    const std::string& cur = (*cflags)[i];
+    if (cur == "-arch") {
+      // This is the first part of a list with ["-arch", "i386"], return the
+      // following item, and delete both of them.
+      if (i < cflags->size() - 1) {
+        std::string ret = (*cflags)[i + 1];
+        cflags->erase(cflags->begin() + i, cflags->begin() + i + 2);
+        return ret;
+      }
+    } else if (StartsWithASCII(cur, "-arch ", true)) {
+      // The arch was passed as one GN string value, e.g. "-arch i386". Return
+      // the stuff following the space and delete the item.
+      std::string ret = cur.substr(6);
+      cflags->erase(cflags->begin() + i);
+      return ret;
+    }
+  }
+  return std::string();
+}
+
 // Finds all values from the given getter from all configs in the given list,
 // and adds them to the given result vector.
 template<typename T>
@@ -350,6 +377,15 @@ void GypBinaryTargetWriter::WriteMacFlags(Flags& flags, int indent) {
 
   Indent(indent) << "'xcode_settings': {\n";
 
+  // Architecture. GYP uses this to write the -arch flag passed to the
+  // compiler, it doesn't look at our -arch flag. So we need to specify it in
+  // this special var and not in the cflags to avoid duplicates or conflicts.
+  std::string arch = GetMacArch(&flags.cflags);
+  if (arch == "i386")
+    Indent(indent + kExtraIndent) << "'ARCHS': [ 'i386' ],\n";
+  else if (arch == "x86_64")
+    Indent(indent + kExtraIndent) << "'ARCHS': [ 'x86_64' ],\n";
+
   // C/C++ flags.
   if (!flags.cflags.empty() || !flags.cflags_c.empty() ||
       !flags.cflags_objc.empty()) {