[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(runtimes)
     # The runtimes target is a configuration of all the runtime libraries
     # together in a single CMake invocaiton.
     llvm_ExternalProject_Add(runtimes
                              ${CMAKE_CURRENT_SOURCE_DIR}
                              DEPENDS ${deps}
                              # Builtins were built separately above
                              CMAKE_ARGS -DCOMPILER_RT_BUILD_BUILTINS=Off
                                         -DLLVM_INCLUDE_TESTS=${LLVM_INCLUDE_TESTS}
+                                        -DLLVM_MAIN_SRC_DIR=${LLVM_MAIN_SRC_DIR}
                              PASSTHROUGH_PREFIXES ${prefixes}
                              EXTRA_TARGETS ${extra_targets}
                                             ${test_targets}
                                             ${SUB_COMPONENTS}
                                             ${SUB_COMPONENT_CHECK_TARGETS}
                                             ${SUB_INSTALL_TARGETS}
                              USE_TOOLCHAIN)
     if(LLVM_INCLUDE_TESTS)
       set_property(GLOBAL APPEND PROPERTY LLVM_ADDITIONAL_TEST_DEPENDS runtimes-test-depends)
       set_property(GLOBAL APPEND PROPERTY LLVM_ADDITIONAL_TEST_TARGETS check-runtimes)
     endif()
   endif()
 endif()