MIPS[64]: Add MIPS support to GN for V8

MIPS support was lacking in GN, only MIPS32 in combination with
CLANG was working properly.
This CL implements support for other flavors of MIPS, for
both CLANG and GCC compilers, in the context of V8 project that
needs it.

Bug: 
Change-Id: Iaa4b4314cafe1631c40d75c151a82d52aa851131
Reviewed-on: https://chromium-review.googlesource.com/677302Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506889}

build/config/compiler/BUILD.gn

@@ -722,6 +722,14 @@ config("compiler_cpu_abi") {
 
       cflags += [ "-m${mips_float_abi}-float" ]
     } else if (current_cpu == "mips" && !is_nacl) {
+      if (is_clang) {
+        cflags += [ "--target=mips-linux-gnu" ]
+        ldflags += [ "--target=mips-linux-gnu" ]
+      } else {
+        cflags += [ "-EB" ]
+        ldflags += [ "-EB" ]
+      }
+
       if (mips_arch_variant == "r6") {
         cflags += [
           "-mips32r6",
@@ -756,16 +764,31 @@ config("compiler_cpu_abi") {
 
       cflags += [ "-m${mips_float_abi}-float" ]
     } else if (current_cpu == "mips64el") {
+      if (is_clang) {
+        if (is_android) {
+          cflags += [ "--target=mips64el-linux-android" ]
+          ldflags += [ "--target=mips64el-linux-android" ]
+        } else {
+          cflags += [ "--target=mips64el-linux-gnuabi64" ]
+          ldflags += [ "--target=mips64el-linux-gnuabi64" ]
+        }
+      } else {
+        cflags += [
+          "-EL",
+          "-mabi=64",
+        ]
+        ldflags += [
+          "-EL",
+          "-mabi=64",
+        ]
+      }
+
       if (mips_arch_variant == "r6") {
         if (is_clang) {
-          if (is_android) {
-            cflags += [
-              "--target=mips64el-linux-android",
-              "-march=mips64el",
-              "-mcpu=mips64r6",
-            ]
-            ldflags += [ "--target=mips64el-linux-android" ]
-          }
+          cflags += [
+            "-march=mips64el",
+            "-mcpu=mips64r6",
+          ]
         } else {
           cflags += [
             "-mips64r6",
@@ -793,12 +816,27 @@ config("compiler_cpu_abi") {
         ]
       }
     } else if (current_cpu == "mips64") {
+      if (is_clang) {
+        cflags += [ "--target=mips64-linux-gnuabi64" ]
+        ldflags += [ "--target=mips64-linux-gnuabi64" ]
+      } else {
+        cflags += [
+          "-EB",
+          "-mabi=64",
+        ]
+        ldflags += [
+          "-EB",
+          "-mabi=64",
+        ]
+      }
+
       if (mips_arch_variant == "r6") {
         cflags += [
           "-mips64r6",
           "-Wa,-mips64r6",
         ]
         ldflags += [ "-mips64r6" ]
+
         if (mips_use_msa == true) {
           cflags += [
             "-mmsa",

build/toolchain/linux/BUILD.gn

@@ -178,12 +178,14 @@ clang_toolchain("clang_mips64el") {
 }
 
 gcc_toolchain("mipsel") {
-  cc = "mipsel-linux-gnu-gcc"
-  cxx = "mipsel-linux-gnu-g++"
-  ar = "mipsel-linux-gnu-ar"
+  toolprefix = "mipsel-linux-gnu-"
+
+  cc = "${toolprefix}gcc"
+  cxx = " ${toolprefix}g++"
+  ar = "${toolprefix}ar"
   ld = cxx
-  readelf = "mipsel-linux-gnu-readelf"
-  nm = "mipsel-linux-gnu-nm"
+  readelf = "${toolprefix}readelf"
+  nm = "${toolprefix}nm"
 
   toolchain_args = {
     cc_wrapper = ""
@@ -195,12 +197,14 @@ gcc_toolchain("mipsel") {
 }
 
 gcc_toolchain("mips64el") {
-  cc = "gcc"
-  cxx = "g++"
-  ar = "ar"
+  toolprefix = "mips64el-linux-gnuabi64-"
+
+  cc = "${toolprefix}gcc"
+  cxx = "${toolprefix}g++"
+  ar = "${toolprefix}ar"
   ld = cxx
-  readelf = "readelf"
-  nm = "nm"
+  readelf = "${toolprefix}readelf"
+  nm = "${toolprefix}nm"
 
   toolchain_args = {
     cc_wrapper = ""
@@ -244,12 +248,14 @@ gcc_toolchain("ppc64") {
 }
 
 gcc_toolchain("mips") {
-  cc = "gcc"
-  cxx = "g++"
+  toolprefix = "mips-linux-gnu-"
 
-  readelf = "readelf"
-  nm = "nm"
-  ar = "ar"
+  cc = "${toolprefix}gcc"
+  cxx = "${toolprefix}g++"
+
+  readelf = "${toolprefix}readelf"
+  nm = "${toolprefix}nm"
+  ar = "${toolprefix}ar"
   ld = cxx
 
   toolchain_args = {
@@ -260,12 +266,14 @@ gcc_toolchain("mips") {
 }
 
 gcc_toolchain("mips64") {
-  cc = "gcc"
-  cxx = "g++"
+  toolprefix = "mips64-linux-gnuabi64-"
 
-  readelf = "readelf"
-  nm = "nm"
-  ar = "ar"
+  cc = "${toolprefix}gcc"
+  cxx = "${toolprefix}g++"
+
+  readelf = "${toolprefix}readelf"
+  nm = "${toolprefix}nm"
+  ar = "${toolprefix}ar"
   ld = cxx
 
   toolchain_args = {