Build llvm with ccache if package is present

This patch has the following changes

The CMake variable LLVM_CCACHE_BUILD is set to OFF by default.
Set this to ON for a ccache enabled build

CCACHE_CPP2 is required to compile the source file directly instead
of compiling the preprocessed file. This will help WERROR is turned ON
for a host clang compiler

The below two options makes more sense in the context of a buildbot

CCACHE_HASHDIR is required to maintain the separate cached data across
builders. This will also help the debuggers to point to the correct source
location

CCACHE_SIZE is important in the perspective of buildbot to increase the
limit on the amount of data to hold in cache for faster compilation

CCACHE_DIR is used to save the cached data to a specific directory.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@277389 91177308-0d34-0410-b5e6-96231b3b80d8

CMakeLists.txt

@@ -101,6 +101,26 @@ if(LLVM_PARALLEL_COMPILE_JOBS)
   endif()
 endif()
 
+# Build llvm with ccache if the package is present
+set(LLVM_CCACHE_BUILD OFF CACHE BOOL "Set to ON for a ccache enabled build")
+if(LLVM_CCACHE_BUILD)
+  find_program(CCACHE_PROGRAM ccache)
+  if(CCACHE_PROGRAM)
+      set(LLVM_CCACHE_SIZE "" CACHE STRING "Size of ccache")
+      set(LLVM_CCACHE_DIR "" CACHE STRING "Directory to keep ccached data")
+      set(CCACHE_PROGRAM "CCACHE_CPP2=yes CCACHE_HASHDIR=yes ${CCACHE_PROGRAM}")
+      if (LLVM_CCACHE_SIZE)
+        set(CCACHE_PROGRAM "CCACHE_SIZE=${LLVM_CCACHE_SIZE} ${CCACHE_PROGRAM}")
+      endif()
+      if (LLVM_CCACHE_DIR)
+        set(CCACHE_PROGRAM "CCACHE_DIR=${LLVM_CCACHE_DIR} ${CCACHE_PROGRAM}")
+      endif()
+      set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE ${CCACHE_PROGRAM})
+  else()
+    message(FATAL_ERROR "Unable to find the program ccache. Set LLVM_CCACHE_BUILD to OFF")
+  endif()
+endif()
+
 option(LLVM_BUILD_GLOBAL_ISEL "Experimental: Build GlobalISel" OFF)
 if(LLVM_BUILD_GLOBAL_ISEL)
   add_definitions(-DLLVM_BUILD_GLOBAL_ISEL)