[HIPIFY][#207][fix] Translate all preprocessor's conditional blocks

+ Start to translate preprocessor's false conditional blocks too:
  based on clang's https://reviews.llvm.org/D66597;
  available only starting from LLVM 10.0 or trunk.
+ Option -skip-excluded-preprocessor-conditional-blocks for skipping excluded conditional blocks:
  the default behavior for hipify-clang built with LLVM < 10.0;
  false by default for hipify-clang built with LLVM 10 or trunk.
+ Add 4 preprocessor unit tests, 2 of which are LLVM 10.0 only
+ Update couple of existing tests by setting -skip-excluded-preprocessor-conditional-blocks option:
  update lit testing accordingly

hipamd/hipify-clang/src/LLVMCompat.cpp

@@ -20,8 +20,13 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 */
 
+#include "ArgParse.h"
 #include "LLVMCompat.h"
 #include "llvm/Support/Path.h"
+#include "clang/Lex/PreprocessorOptions.h"
+#include "clang/Frontend/CompilerInstance.h"
+
+const std::string sHipify = "[HIPIFY] ", sConflict = "conflict: ", sError = "error: ", sWarning = "warning: ";
 
 namespace llcompat {
 
@@ -122,4 +127,20 @@ bool pragma_once_outside_header() {
 #endif
 }
 
+void RetainExcludedConditionalBlocks(clang::CompilerInstance &CI) {
+#if LLVM_VERSION_MAJOR > 9
+  clang::PreprocessorOptions &PPOpts = CI.getPreprocessorOpts();
+  PPOpts.RetainExcludedConditionalBlocks = !SkipExcludedPPConditionalBlocks;
+#endif
+}
+
+bool CheckCompatibility() {
+#if LLVM_VERSION_MAJOR < 10
+  if (SkipExcludedPPConditionalBlocks) {
+    llvm::errs() << "\n" << sHipify << sWarning << "Option '" << SkipExcludedPPConditionalBlocks.ArgStr.str() << "' is supported starting from LLVM version 10.0\n";
+  }
+#endif
+  return true;
+}
+
 } // namespace llcompat