[Libomptarget] Fix lookup of the libcgpu.a library

Summary:
The `libcgpu.a` library was added to support certain libc functions. A
recent patch made us pass its location directly on the commandline,
however it used `find_library`. This doesn't work because the ordering
of CMake might run `fine_library` before it builds the library we're
trying to find. This patch changes this to just use the destimation we
know it will end up in and checks it manually.

openmp/libomptarget/CMakeLists.txt

@@ -96,15 +96,6 @@ if("libc" IN_LIST LLVM_ENABLE_RUNTIMES AND (LIBC_GPU_BUILD OR
   set(LIBC_GPU_SUPPORT TRUE)
 endif()
 
-# Find the path of the GPU libc static library.
-find_library(GPU_LIBC_PATH NAMES cgpu
-             PATHS ${LIBOMPTARGET_LLVM_LIBRARY_DIR} NO_DEFAULT_PATH)
-if((NOT GPU_LIBC_PATH) OR (NOT LIBC_GPU_SUPPORT))
-  set(GPU_LIBC_PATH "")
-endif()
-
-set(LIBOMPTARGET_GPU_LIBC_PATH  ${GPU_LIBC_PATH} CACHE STRING
-    "Location of the 'libcgpu.a' library ")
 set(LIBOMPTARGET_GPU_LIBC_SUPPORT ${LIBC_GPU_SUPPORT} CACHE BOOL
     "Libomptarget support for the GPU libc")
 pythonize_bool(LIBOMPTARGET_GPU_LIBC_SUPPORT)

openmp/libomptarget/test/lit.cfg

@@ -153,8 +153,10 @@ def remove_suffix_if_present(name):
         return name
 
 def add_libraries(source):
-    return source + " " + config.libomptarget_libc_path + " " + \
-           config.library_dir + "/libomptarget.devicertl.a"
+    if config.libomptarget_has_libc:
+        return source + " " + config.llvm_library_dir + "/libcgpu.a " + \
+               config.library_dir + "/libomptarget.devicertl.a"
+    return source + " " + config.library_dir + "/libomptarget.devicertl.a"
 
 # substitutions
 # - for targets that exist in the system create the actual command.

openmp/libomptarget/test/lit.site.cfg.in

@@ -12,6 +12,7 @@ config.cuda_libdir = "@CUDA_LIBDIR@"
 config.cuda_test_arch = "@LIBOMPTARGET_DEP_CUDA_ARCH@"
 config.libomptarget_obj_root = "@CMAKE_CURRENT_BINARY_DIR@/@CURRENT_TARGET@"
 config.library_dir = "@LIBOMPTARGET_LIBRARY_DIR@"
+config.llvm_library_dir = "@LIBOMPTARGET_LLVM_LIBRARY_DIR@"
 config.omp_header_directory = "@LIBOMPTARGET_OPENMP_HEADER_FOLDER@"
 config.omp_host_rtl_directory = "@LIBOMPTARGET_OPENMP_HOST_RTL_FOLDER@"
 config.llvm_lib_directory = "@LIBOMPTARGET_LLVM_LIBRARY_DIR@"
@@ -23,7 +24,6 @@ config.libomptarget_not = "@OPENMP_NOT_EXECUTABLE@"
 config.libomptarget_debug = @LIBOMPTARGET_DEBUG@
 config.has_libomptarget_ompt = @LIBOMPTARGET_OMPT_SUPPORT@
 config.libomptarget_has_libc = @LIBOMPTARGET_GPU_LIBC_SUPPORT@
-config.libomptarget_libc_path = "@LIBOMPTARGET_GPU_LIBC_PATH@"
 
 # Let the main config do the real work.
 lit_config.load_config(config, "@CMAKE_CURRENT_SOURCE_DIR@/lit.cfg")