[compiler-rt] Pass the CMake binary dir directly (llvm#102493)

Summary:
The usage of `LLVM_CMAKE_DIR` is confusing in CMake, because in LLVM it
refers to `llvm/cmake/modules/` while compiler-rt wants the `build/` dir
for finding LLVM. THis passes it manually.

Author: jhuber6

llvm/runtimes/CMakeLists.txt

@@ -89,6 +89,7 @@ function(builtin_default_target compiler_rt_path)
                                       -DLLVM_RUNTIME_OUTPUT_INTDIR=${LLVM_TOOLS_BINARY_DIR}
                                       -DLLVM_DEFAULT_TARGET_TRIPLE=${LLVM_TARGET_TRIPLE}
                                       -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=${LLVM_ENABLE_PER_TARGET_RUNTIME_DIR}
+                                      -DLLVM_CMAKE_DIR=${CMAKE_BINARY_DIR}
                                       -DCMAKE_C_COMPILER_WORKS=ON
                                       -DCMAKE_ASM_COMPILER_WORKS=ON
                                       ${COMMON_CMAKE_ARGS}
@@ -128,6 +129,7 @@ function(builtin_register_target compiler_rt_path name)
                            CMAKE_ARGS -DLLVM_LIBRARY_OUTPUT_INTDIR=${LLVM_LIBRARY_DIR}
                                       -DLLVM_RUNTIME_OUTPUT_INTDIR=${LLVM_TOOLS_BINARY_DIR}
                                       -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON
+                                      -DLLVM_CMAKE_DIR=${CMAKE_BINARY_DIR}
                                       -DCMAKE_C_COMPILER_WORKS=ON
                                       -DCMAKE_ASM_COMPILER_WORKS=ON
                                       -DCOMPILER_RT_DEFAULT_TARGET_ONLY=ON