[CMake] Fixing lit for runtimes directory

[Hahnfeld]

Summary

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.

[beanz]

LLVMConfig.cmake does have LLVM_BUILD_MAIN_SRC_DIR which is set to the value of LLVM_MAIN_SRC_DIR, so we should instead just do set(LLVM_MAIN_SRC_DIR ${LLVM_BUILD_MAIN_SRC_DIR}) around line 60 where we map up the other variables that don't match between in-tree builds and LLVMConfig.cmake.

[Hahnfeld]

In D24503#541407, @beanz wrote:

LLVMConfig.cmake does have LLVM_BUILD_MAIN_SRC_DIR which is set to the value of LLVM_MAIN_SRC_DIR, so we should instead just do set(LLVM_MAIN_SRC_DIR ${LLVM_BUILD_MAIN_SRC_DIR}) around line 60 where we map up the other variables that don't match between in-tree builds and LLVMConfig.cmake.

Ah thanks, that looks much better!

[beanz]

LGTM!

runtimes/CMakeLists.txt

if(${CMAKE_SOURCE_DIR} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR})
   # either from a build directory or an installed LLVM.
   include(LLVMConfig)
 
   # Setting these variables will allow the sub-build to put their outputs into
   # the library and bin directories of the top-level build.
   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)
 
     # TODO: Clean this up as part of an interface standardization
     string(REPLACE "-" "_" canon_name ${projName})
     string(TOUPPER ${canon_name} canon_name)
     # The subdirectories need to treat this as standalone builds
     set(${canon_name}_STANDALONE_BUILD On)