More doxygen/documentation cleanups.

This reduces the number of warnings generated by Doxygen by about 100
(roughly 10%).  Issues addressed:
(1) Primarily, backslash-escaped "@foo" and "#bah" in Doxygen comments
when they're not supposed to be Doxygen commands or links, and
similarly for "<baz>" when it's not intended as as HTML tag;
(2) Changed some \t commands (which don't exist) to \c ("to refer to a
word of code", as the Doxygen manual says);
(3) \precondition becomes \pre;
(4) When touching comments, deleted a couple of spurious spaces in them;
(5) Changed some \n and \r to \\n and \\r;
(6) Fixed one tiny typo: #pragms -> #pragma.

This patch touches documentation/comments only.

llvm-svn: 158422

clang/lib/Frontend/InitPreprocessor.cpp

@@ -49,7 +49,7 @@ static void DefineBuiltinMacro(MacroBuilder &Builder, StringRef Macro,
   }
 }
 
-/// AddImplicitInclude - Add an implicit #include of the specified file to the
+/// AddImplicitInclude - Add an implicit \#include of the specified file to the
 /// predefines buffer.
 static void AddImplicitInclude(MacroBuilder &Builder, StringRef File,
                                FileManager &FileMgr) {
@@ -66,8 +66,8 @@ static void AddImplicitIncludeMacros(MacroBuilder &Builder,
   Builder.append("##"); // ##?
 }
 
-/// AddImplicitIncludePTH - Add an implicit #include using the original file
-///  used to generate a PTH cache.
+/// AddImplicitIncludePTH - Add an implicit \#include using the original file
+/// used to generate a PTH cache.
 static void AddImplicitIncludePTH(MacroBuilder &Builder, Preprocessor &PP,
                                   StringRef ImplicitIncludePTH) {
   PTHManager *P = PP.getPTHManager();