clang/arm: Use integrated assembler for boringssl for arm_version 6.

An arm_version 6 file assumes that __clang__ means that clang's assembler is
being used, while it only really identifies clang is used as preprocessor.

Luckily, it looks like only the armv7 assembly code in boringssl is incompatible
with clang's built-in assembler.

BUG=732066,124610
TBR=davidben

Review-Url: https://codereview.chromium.org/2932043004
Cr-Commit-Position: refs/heads/master@{#478524}

third_party/boringssl/BUILD.gn

@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
+import("//build/config/arm.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build_overrides/build.gni")
 import("//testing/libfuzzer/fuzzer_test.gni")
@@ -65,7 +66,7 @@ if (is_win && !is_msan) {
     include_dirs = [ "src/include" ]
 
     if ((current_cpu == "arm" || current_cpu == "arm64") && is_clang) {
-      if (current_cpu == "arm") {
+      if (current_cpu == "arm" && arm_version != 6) {
         # TODO(hans) Enable integrated-as (crbug.com/124610).
         asmflags += [ "-fno-integrated-as" ]
       }