GN: Harmonize ARM compiler settings with GYP

This changes various defaults about the ARM compiler setup so
that GN matches what GYP does today:
* Prefix for cross tools is arm-linux-gnueabihf- not arm-linux-gnueabi-
* arm_float_abi defaults to hard for non-Android ARMv7
* Non-CrOS ARM builds use the ARM sysroot by default
  (the one installed by install-build-deps.sh --arm)
* Define a clang_arm toolchain, pass it the -no-integrated and
  -target arm-linux-gnueabihf and switches as GYP does

R=dpranke@chromium.org, sbc@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1352313002

Cr-Commit-Position: refs/heads/master@{#350100}

1 files changed, 25 insertions, 5 deletions

diff --git a/build/toolchain/linux/BUILD.gn b/build/toolchain/linux/BUILD.gn
index 94d9a16..84a790d 100644
--- a/build/toolchain/linux/BUILD.gn
+++ b/build/toolchain/linux/BUILD.gn
@@ -16,14 +16,34 @@ if (use_goma) {
   compiler_prefix = ""
 }
 
+gcc_toolchain("clang_arm") {
+  prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
+                       root_build_dir)
+  cc = "${compiler_prefix}$prefix/clang"
+  cxx = "${compiler_prefix}$prefix/clang++"
+
+  toolprefix = "arm-linux-gnueabihf-"
+  readelf = "${toolprefix}readelf"
+  ar = "${toolprefix}ar"
+  ld = cxx
+  readelf = "${toolprefix}readelf"
+  nm = "${toolprefix}nm"
+
+  toolchain_cpu = "arm"
+  toolchain_os = "linux"
+  is_clang = true
+}
+
 gcc_toolchain("arm") {
-  cc = "${compiler_prefix}arm-linux-gnueabi-gcc"
-  cxx = "${compiler_prefix}arm-linux-gnueabi-g++"
+  toolprefix = "arm-linux-gnueabihf-"
+
+  cc = "${compiler_prefix}${toolprefix}gcc"
+  cxx = "${compiler_prefix}${toolprefix}g++"
 
-  ar = "arm-linux-gnueabi-ar"
+  ar = "${toolprefix}ar"
   ld = cxx
-  readelf = "arm-linux-gnueabi-readelf"
-  nm = "arm-linux-gnueabi-nm"
+  readelf = "${toolprefix}readelf"
+  nm = "${toolprefix}nm"
 
   toolchain_cpu = "arm"
   toolchain_os = "linux"