Roll buildtools forward and fix GN build for it.

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 8efdd5c85fdabdf5e024a2dcc04ecc3340c838a3..d77a921bd4d9333ffd18ea088fbbce8ff6788495 100644
--- a/build/toolchain/mac/BUILD.gn
+++ b/build/toolchain/mac/BUILD.gn
@@ -85,7 +85,7 @@ template("mac_toolchain") {
     tool("asm") {
       # For GCC we can just use the C compiler to compile assembly.
       depfile = "{{output}}.d"
-      command = "$cc -MMD -MF $depfile {{defines}} {{include_dirs}} $sysroot_flags $toolchain_flags {{cflags}} {{cflags_c}} -c {{source}} -o {{output}}"
+      command = "$cc -MMD -MF $depfile {{defines}} {{include_dirs}} $sysroot_flags $toolchain_flags {{asmflags}} -c {{source}} -o {{output}}"
       depsformat = "gcc"
       description = "ASM {{output}}"
       outputs = [
@@ -193,7 +193,7 @@ template("mac_toolchain") {
       description = "COPY {{source}} {{output}}"
     }
 
-    toolchain_args() {
+    toolchain_args = {
       current_cpu = invoker.toolchain_cpu
       current_os = invoker.toolchain_os