Introduce CC/CXX/JAVAC_WRAPPER to wrap the calls to clang.

This is essentially Ide800c24f0c2ebbb1cfb358bd8f99ec8a9d41253
applied to clang.

Change-Id: I883f9e9a31fff50a64568a06ef5248437344542b
diff --git a/core/clang/config.mk b/core/clang/config.mk
index 10b4d72..07ad60e 100644
--- a/core/clang/config.mk
+++ b/core/clang/config.mk
@@ -22,6 +22,17 @@
 CLANG_TBLGEN := $(HOST_OUT_EXECUTABLES)/clang-tblgen$(BUILD_EXECUTABLE_SUFFIX)
 LLVM_TBLGEN := $(HOST_OUT_EXECUTABLES)/llvm-tblgen$(BUILD_EXECUTABLE_SUFFIX)
 
+# The C/C++ compiler can be wrapped by setting the CC/CXX_WRAPPER vars.
+ifdef CC_WRAPPER
+  ifneq ($(CC_WRAPPER),$(firstword $(CLANG)))
+    CLANG := $(CC_WRAPPER) $(CLANG)
+  endif
+endif
+ifdef CXX_WRAPPER
+  ifneq ($(CXX_WRAPPER),$(firstword $(CLANG_CXX)))
+    CLANG_CXX := $(CXX_WRAPPER) $(CLANG_CXX)
+  endif
+endif
 
 # Clang flags for all host or target rules
 CLANG_CONFIG_EXTRA_ASFLAGS :=