Roll buildtools forward and fix GN build for it.

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 5bc242f631f51073eb275e8bf9a7a5b21da498e5..7f7e42373cb6433928d467cbefc2846dc629f708 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -53,6 +53,7 @@ if (!is_win) {
 # where stuff should go. Put warning related stuff in the "warnings" config.
 
 config("compiler") {
+  asmflags = []
   cflags = []
   cflags_c = []
   cflags_cc = []
@@ -447,6 +448,14 @@ config("compiler") {
       }
     }
   }
+
+  # Assign any flags set for the C compiler to asmflags so that they are sent
+  # to the assembler. The Windows assembler takes different types of flags
+  # so only do so for posix platforms.
+  if (is_posix) {
+    asmflags += cflags
+    asmflags += cflags_c
+  }
 }
 
 config("compiler_arm_fpu") {