[clang] Add __has_feature(swiftcc) support

This patch adds `swiftcc` feature to check if the target supports Swift
calling convention as well as we do for `swiftasynccc`.

Author: kateinoigakukun

clang/include/clang/Basic/Features.def

@@ -102,6 +102,9 @@ FEATURE(memory_sanitizer,
 FEATURE(thread_sanitizer, LangOpts.Sanitize.has(SanitizerKind::Thread))
 FEATURE(dataflow_sanitizer, LangOpts.Sanitize.has(SanitizerKind::DataFlow))
 FEATURE(scudo, LangOpts.Sanitize.hasOneOf(SanitizerKind::Scudo))
+FEATURE(swiftcc,
+  PP.getTargetInfo().checkCallingConvention(CC_Swift) ==
+  clang::TargetInfo::CCCR_OK)
 FEATURE(swiftasynccc,
   PP.getTargetInfo().checkCallingConvention(CC_SwiftAsync) ==
   clang::TargetInfo::CCCR_OK)

clang/test/Sema/swift-call-conv.c

@@ -1,7 +1,12 @@
 // RUN: %clang_cc1 -triple aarch64-unknown-windows-msvc -fsyntax-only %s -verify
 // RUN: %clang_cc1 -triple thumbv7-unknown-windows-msvc -fsyntax-only %s -verify
 // RUN: %clang_cc1 -triple x86_64-unknown-windows-msvc -fsyntax-only %s -verify
+// RISC-V does not support swiftcall
+// RUN: %clang_cc1 -triple riscv32-unknown-elf -fsyntax-only %s -verify
 
+#if __has_feature(swiftcc)
 // expected-no-diagnostics
-
+#else
+// expected-warning@+2 {{'__swiftcall__' calling convention is not supported for this target}}
+#endif
 void __attribute__((__swiftcall__)) f(void) {}