Fix mixed MSVC/clang-cl build (#1617)

Summary:
An executable built by clang-cl that is linked against folly/logging
from vcpkg will fail to link due to a few missing symbols.  folly/logging
has a number of functions that are only defined when `__INCLUDE_LEVEL__` is defined.
vcpkg always uses MSVC, MSVC does not support this macro while clang-cl does,
resulting in mismatch between what is defined, used, and declared.

These ifdefs mostly came from fc507b26.

The (minor IMO) negative consequence of this diff is that
`XlogFileScopeInfo` will be unnecessarily larger (a pointer and an uint32)
 on compilers that don't support `__INCLUDE_LEVEL__` (e.g MSVC).

The actual condition of whether to make use of `__INCLUDE_LEVEL__` remains, via the `XLOG_IS_IN_HEADER_FILE` macro.

Pull Request resolved: https://github.com/facebook/folly/pull/1617

Reviewed By: yfeldblum

Differential Revision: D29753787

Pulled By: Orvid

fbshipit-source-id: 28f8128c981b255960d7838d2df2a3d299153bc2

folly/logging/LogStreamProcessor.cpp

@@ -111,7 +111,6 @@ LogStreamProcessor::LogStreamProcessor(
       message_{std::move(msg)},
       stream_{this} {}
 
-#ifdef __INCLUDE_LEVEL__
 namespace {
 LogCategory* getXlogCategory(XlogFileScopeInfo* fileScopeInfo) {
   // By the time a LogStreamProcessor is created, the XlogFileScopeInfo object
@@ -165,7 +164,6 @@ LogStreamProcessor::LogStreamProcessor(
           functionName,
           INTERNAL,
           std::string()) {}
-#endif
 
 /*
  * We intentionally define the LogStreamProcessor destructor in

folly/logging/LogStreamProcessor.h

@@ -186,7 +186,6 @@ class LogStreamProcessor {
             INTERNAL,
             formatLogString(fmt, std::forward<Args>(args)...)) {}
 
-#ifdef __INCLUDE_LEVEL__
   /*
    * Versions of the above constructors to use in XLOG() macros that appear in
    * .cpp files.  These are only used if the compiler supports the
@@ -254,7 +253,6 @@ class LogStreamProcessor {
             functionName,
             INTERNAL,
             formatLogString(fmt, std::forward<Args>(args)...)) {}
-#endif
 
   ~LogStreamProcessor() noexcept;
 

folly/logging/xlog.cpp

@@ -123,7 +123,6 @@ LogCategory* XlogCategoryInfo<IsInHeaderFile>::init(
       &isInitialized_);
 }
 
-#ifdef __INCLUDE_LEVEL__
 LogLevel XlogLevelInfo<false>::loadLevelFull(
     folly::StringPiece categoryName,
     bool isOverridden,
@@ -137,12 +136,8 @@ LogLevel XlogLevelInfo<false>::loadLevelFull(
   }
   return currentLevel;
 }
-#endif
 
 // Explicitly instantiations of XlogLevelInfo and XlogCategoryInfo
-// If __INCLUDE_LEVEL__ is not available only the "true" variants ever get
-// used, because we cannot determine if we are ever in the .cpp file being
-// compiled or not.
 template class XlogLevelInfo<true>;
 template class XlogCategoryInfo<true>;
 } // namespace folly

folly/logging/xlog.h

@@ -636,10 +636,8 @@ namespace folly {
 
 class XlogFileScopeInfo {
  public:
-#ifdef __INCLUDE_LEVEL__
   std::atomic<::folly::LogLevel> level;
   ::folly::LogCategory* category;
-#endif
 };
 
 /**
@@ -712,7 +710,6 @@ class XlogCategoryInfo {
   LogCategory* category_;
 };
 
-#ifdef __INCLUDE_LEVEL__
 /**
  * Specialization of XlogLevelInfo for XLOG() statements in the .cpp file being
  * compiled.  In this case we only define a single file-static LogLevel object
@@ -765,7 +762,6 @@ class XlogCategoryInfo<false> {
     return fileScopeInfo;
   }
 };
-#endif
 
 /**
  * Get the default XLOG() category name for the given filename.