[CMake] Factor the setting of LLVM_BUILD_MODE to a macro so that we can re-use it in compiler-rt

[gbedwell]

Summary

This is essentially an NFC as it stands, but is required for a followup patch where the new macro is used from part of the compiler-rt CMake system. I'll cross-reference the patches shortly.

[gbedwell]

See https://reviews.llvm.org/D38471 for the follow-up that this commit is a pre-requisite for.

[rnk]

lgtm

cmake/modules/AddLLVM.cmake

foreach(var ${ARGN})
     if(${var})
       set(${var} 1 PARENT_SCOPE)
     else()
       set(${var} 0 PARENT_SCOPE)
     endif()
   endforeach()
 endfunction(llvm_canonicalize_cmake_booleans)
 
+macro(set_llvm_build_mode)
+  # Configuration-time: See Unit/lit.site.cfg.in
+  if (CMAKE_CFG_INTDIR STREQUAL ".")
+    set(LLVM_BUILD_MODE ".")
+  else ()
+    set(LLVM_BUILD_MODE "%(build_mode)s")
+  endif ()
+endmacro()
+
 # This function provides an automatic way to 'configure'-like generate a file
 # based on a set of common and custom variables, specifically targeting the
 # variables needed for the 'lit.site.cfg' files. This function bundles the
 # common variables that any Lit instance is likely to need, and custom
 # variables can be passed in.
 function(configure_lit_site_cfg site_in site_out)
   cmake_parse_arguments(ARG "" "" "MAIN_CONFIG;OUTPUT_MAPPING" ${ARGN})
 
   if ("${ARG_MAIN_CONFIG}" STREQUAL "")
     get_filename_component(INPUT_DIR ${site_in} DIRECTORY)
     set(ARG_MAIN_CONFIG "${INPUT_DIR}/lit.cfg")
   endif()
   if ("${ARG_OUTPUT_MAPPING}" STREQUAL "")
     set(ARG_OUTPUT_MAPPING "${site_out}")
   endif()
 
   foreach(c ${LLVM_TARGETS_TO_BUILD})
     set(TARGETS_BUILT "${TARGETS_BUILT} ${c}")
   endforeach(c)
   set(TARGETS_TO_BUILD ${TARGETS_BUILT})
 
   set(SHLIBEXT "${LTDL_SHLIB_EXT}")
 
-  # Configuration-time: See Unit/lit.site.cfg.in
-  if (CMAKE_CFG_INTDIR STREQUAL ".")
-    set(LLVM_BUILD_MODE ".")
-  else ()
-    set(LLVM_BUILD_MODE "%(build_mode)s")
-  endif ()
+  set_llvm_build_mode()
 
   # They below might not be the build tree but provided binary tree.
   set(LLVM_SOURCE_DIR ${LLVM_MAIN_SRC_DIR})
   set(LLVM_BINARY_DIR ${LLVM_BINARY_DIR})
   string(REPLACE "${CMAKE_CFG_INTDIR}" "${LLVM_BUILD_MODE}" LLVM_TOOLS_DIR "${LLVM_TOOLS_BINARY_DIR}")
   string(REPLACE ${CMAKE_CFG_INTDIR} ${LLVM_BUILD_MODE} LLVM_LIBS_DIR  "${LLVM_LIBRARY_DIR}")
 
   # SHLIBDIR points the build tree.