Subzero: Fix Makefile.standalone to enable format with DEBUG flag

When building pnacl with --host-flavor=debug, tools at

../../out/llvm_x86_64_linux_work/Release+Asserts/bin

are not available, so we need a fix to enable source code formatting
with tools from

../../out/llvm_x86_64_linux_debug_work/Debug+Asserts/bin

R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/2081223003 .

Patch from Srdjan Obucina <Srdjan.Obucina@imgtec.com>.
diff --git a/Makefile.standalone b/Makefile.standalone
index 201a8e4..3164798 100644
--- a/Makefile.standalone
+++ b/Makefile.standalone
@@ -219,7 +219,13 @@
   # LLVM autoconf build
   LLVM_LIBS := -lLLVM-3.7svn
   GTEST_LIB_PATH ?= -L../../out/llvm_x86_64_linux_work/Release+Asserts/lib
-  CLANG_FORMAT_PATH ?= ../../out/llvm_x86_64_linux_work/Release+Asserts/bin
+  ifneq ($(wildcard \
+           ../../out/llvm_x86_64_linux_work/Release+Asserts/bin/clang-format),)
+    CLANG_FORMAT_PATH ?= ../../out/llvm_x86_64_linux_work/Release+Asserts/bin
+  else
+    CLANG_FORMAT_PATH ?= \
+                     ../../out/llvm_x86_64_linux_debug_work/Debug+Asserts/bin
+  endif
 endif
 
 LLVM_LDFLAGS := $(LLVM_LIBS) \