win: Call clang-cl instead of clang-cl.exe when targeting win on a non-win host.

No behavior change, since non-win hosts targeting windows currently don't
exist. But if they did, there are three choices for how to invoke the compiler:

1. Call the compiler on the host clang-cl.exe instead of clang-cl.  That's weird
   because clang-cl is a host-native binary.

2. Don't append ".exe" to any program in build/toolchain/win/BUILD.gn -- it's
   probably not needed on Windows.  But if we end up running real Windows
   binaries on non-Windows (e.g. midl.exe through wine), then those would
   have a .exe extension on the non-Windows host.

3. Do what this CL does. This seems nicest.

BUG=495204

Review URL: https://codereview.chromium.org/1585113007

Cr-Commit-Position: refs/heads/master@{#369854}

1 files changed, 8 insertions, 2 deletions

diff --git a/build/toolchain/win/BUILD.gn b/build/toolchain/win/BUILD.gn
index 0233353..4fb7279 100644
--- a/build/toolchain/win/BUILD.gn
+++ b/build/toolchain/win/BUILD.gn
@@ -235,6 +235,12 @@ template("msvc_toolchain") {
   }
 }
 
+if (host_os == "win") {
+  clang_cl = "clang-cl.exe"
+} else {
+  clang_cl = "clang-cl"
+}
+
 # 32-bit toolchains. Only define these when the target architecture is 32-bit
 # since we don't do any 32-bit cross compiles when targeting 64-bit (the
 # build does generate some 64-bit stuff from 32-bit target builds).
@@ -261,7 +267,7 @@ if (target_cpu == "x86") {
     toolchain_cpu = "x86"
     prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
                          root_build_dir)
-    cl = "${goma_prefix}$prefix/clang-cl.exe"
+    cl = "${goma_prefix}$prefix/${clang_cl}"
     toolchain_os = "win"
     is_clang = true
   }
@@ -290,7 +296,7 @@ msvc_toolchain("clang_x64") {
   toolchain_cpu = "x64"
   prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
                        root_build_dir)
-  cl = "${goma_prefix}$prefix/clang-cl.exe"
+  cl = "${goma_prefix}$prefix/${clang_cl}"
   toolchain_os = "win"
   is_clang = true
 }