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

This reverts commit a4f84fdfed9a805d69b37de997512cd0616b3ff8.
Added "export CCACHE_CPP2 := true" to work around ccache bug with clang.
See:
http://petereisentraut.blogspot.com/2011/09/ccache-and-clang-part-2.html

Change-Id: I2b1fa8fd59c3a113c4028a92a1d16018133c9792
diff --git a/core/clang/config.mk b/core/clang/config.mk
index 1de46f0..c1625f2 100644
--- a/core/clang/config.mk
+++ b/core/clang/config.mk
@@ -17,6 +17,17 @@
 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 :=
diff --git a/core/combo/select.mk b/core/combo/select.mk
index e18cb1b..d495c6f 100644
--- a/core/combo/select.mk
+++ b/core/combo/select.mk
@@ -82,6 +82,10 @@
   # on a workstation.
   export CCACHE_BASEDIR := /
 
+  # Workaround for ccache with clang.
+  # See http://petereisentraut.blogspot.com/2011/09/ccache-and-clang-part-2.html
+  export CCACHE_CPP2 := true
+
   CCACHE_HOST_TAG := $(HOST_PREBUILT_TAG)
   # If we are cross-compiling Windows binaries on Linux
   # then use the linux ccache binary instead.