[CMake] Fixing lit for runtimes directory

Copy variable LLVM_BUILD_MAIN_SRC_DIR from LLVMConfig.cmake to
LLVM_MAIN_SRC_DIR as it is named for in-tree builds. This ensures that
add_lit_target() can reliably find llvm-lit which is not necessarily
in the PATH.

Differential Revision: https://reviews.llvm.org/D24503

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@281585 91177308-0d34-0410-b5e6-96231b3b80d8

runtimes/CMakeLists.txt

@@ -58,6 +58,9 @@ if(${CMAKE_SOURCE_DIR} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR})
   set(LLVM_LIBRARY_OUTPUT_INTDIR ${LLVM_LIBRARY_DIR})
   set(LLVM_RUNTIME_OUTPUT_INTDIR ${LLVM_TOOLS_BINARY_DIR})
 
+  # This variable makes sure that e.g. llvm-lit is found.
+  set(LLVM_MAIN_SRC_DIR ${LLVM_BUILD_MAIN_SRC_DIR})
+
   foreach(entry ${runtimes})
     get_filename_component(projName ${entry} NAME)