win: Fix upperilm header generation

clang-cl doesn't recognize "-P -E -x c" compiler arguments,
we should use MSVC version of them "/E /TC".

Seems clang-cl is not able to handle /P /E together
so I only left the necessary one.

Fixes: #1192

Author: kaadam

tools/flang2/utils/upper/CMakeLists.txt

@@ -12,7 +12,14 @@ add_executable(upperl
 # FIXME: Preprocessing and sorting should be part of add_custom_command below.
 get_property(cdefs DIRECTORY PROPERTY COMPILE_DEFINITIONS)
 list(TRANSFORM cdefs PREPEND "-D")
-execute_process(COMMAND "${CMAKE_C_COMPILER}" -E -P -x c ${cdefs} ${UTILS_UPPER_DIR}/upperilm.in
+
+if (NOT MSVC  OR "${CMAKE_C_COMPILER_FRONTEND_VARIANT}" STREQUAL "GNU")
+  set(COMPILER_ARGUMENTS -E -P -x c)
+else()
+  set(COMPILER_ARGUMENTS /E /TC)
+endif()
+
+execute_process(COMMAND "${CMAKE_C_COMPILER}" ${COMPILER_ARGUMENTS} ${cdefs} ${UTILS_UPPER_DIR}/upperilm.in
   WORKING_DIRECTORY ${UTILS_UPPER_BIN_DIR}
   RESULT_VARIABLE cpp_result
   OUTPUT_VARIABLE cpp_output