SourceKit: adapt for SVN r284681

LLVM SVN r284681 replaced `LLVM_FUNCTION_NAME` with `__func__` as all supported
compilers support that keyword now.  The holdout was MSVC, and swift requires
clang, so this is always supported.  NFC.

Author: compnerd

tools/SourceKit/include/SourceKit/Support/Logging.h

@@ -105,7 +105,7 @@ class Logger : public llvm::RefCountedBase<Logger> {
 /// \endcode
 #define LOG_SECTION(NAME, LEVEL) \
   if (LogRef Log = SourceKit::Logger::make(NAME, SourceKit::Logger::Level::LEVEL))
-#define LOG_FUNC_SECTION(LEVEL) LOG_SECTION(LLVM_FUNCTION_NAME, LEVEL)
+#define LOG_FUNC_SECTION(LEVEL) LOG_SECTION(__func__, LEVEL)
 #define LOG_FUNC_SECTION_WARN LOG_FUNC_SECTION(Warning)
 
 #define LOG(NAME, LEVEL, msg) LOG_SECTION(NAME, LEVEL) \