[OpenMP] Avoid using CPU-specific flags for GPU

Since commit be6f110 we lost a few
workarounds that prevented CPU-specific flags to leak from CXXFLAGS to a
binary targetting GPUs causing errors and/or warnings.

Re-add those workarounds and expand them with -mtune,
-mbranch-protection and -fcf-protection.

Author: tuliom

openmp/device/CMakeLists.txt

@@ -36,6 +36,13 @@ list(APPEND compile_options -Wno-unknown-cuda-version)
 if(LLVM_DEFAULT_TARGET_TRIPLE)
   list(APPEND compile_options --target=${LLVM_DEFAULT_TARGET_TRIPLE})
 endif()
+# Ensure that CPU-related parameters won't be brought in.
+string(REGEX REPLACE "-mcpu[^ \t\r\n]*" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
+string(REGEX REPLACE "-march[^ \t\r\n]*" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
+string(REGEX REPLACE "-mtune[^ \t\r\n]*" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
+string(REGEX REPLACE "-mbranch-protection[^ \t\r\n]*" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
+string(REGEX REPLACE "-fcf-protection[^ \t\r\n]*" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
+list(APPEND compile_options -Wno-unused-command-line-argument)
 
 # We disable the slp vectorizer during the runtime optimization to avoid
 # vectorized accesses to the shared state. Generally, those are "good" but