MIPS64: Add clang compile flags for MIPS64r6

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 2f107f7d3bc3d83d578a93a1d9cd4a53c1292eb2..92e2dba3128f2c82922b370b95c5f8b3f8673764 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -342,7 +342,8 @@ config("compiler") {
     # Gold is the default linker for the bundled binutils so we explicitly
     # enable the bfd linker when use_gold is not set.
     ldflags += [ "-fuse-ld=bfd" ]
-  } else if (is_android && current_cpu == "mipsel" && is_clang) {
+  } else if (is_android && is_clang &&
+             (current_cpu == "mipsel" || current_cpu == "mips64el")) {
     # Let clang find the ld.bfd in the NDK.
     _rebased_android_toolchain_root =
         rebase_path(android_toolchain_root, root_build_dir)
@@ -618,11 +619,22 @@ config("compiler_cpu_abi") {
       cflags += [ "-m${mips_float_abi}-float" ]
     } else if (current_cpu == "mips64el") {
       if (mips_arch_variant == "r6") {
-        cflags += [
-          "-mips64r6",
-          "-Wa,-mips64r6",
-        ]
-        ldflags += [ "-mips64r6" ]
+        if (is_clang) {
+          if (is_android) {
+            cflags += [
+              "--target=mips64el-linux-android",
+              "-march=mips64el",
+              "-mcpu=mips64r6",
+            ]
+            ldflags += [ "--target=mips64el-linux-android" ]
+          }
+        } else {
+          cflags += [
+            "-mips64r6",
+            "-Wa,-mips64r6",
+          ]
+          ldflags += [ "-mips64r6" ]
+        }
       } else if (mips_arch_variant == "r2") {
         cflags += [
           "-mips64r2",