Rip out old workarounds, hacks and macros for newer C++ features not being supported back in the day.

Adds LL_COMPILE_TIME_MESSAGE support to Linux.

llfinite -> std::isfinite
llisnan -> std::isnan
vector_shrink_to_fit -> vector.shrink_to_fit

indra/llmessage/llbufferstream.cpp

@@ -233,17 +233,10 @@ int LLBufferStreamBuf::sync()
 }
 
 // virtual
-#if( LL_WINDOWS || __GNUC__ > 2)
 LLBufferStreamBuf::pos_type LLBufferStreamBuf::seekoff(
 	LLBufferStreamBuf::off_type off,
 	std::ios::seekdir way,
 	std::ios::openmode which)
-#else
-streampos LLBufferStreamBuf::seekoff(
-	streamoff off,
-	std::ios::seekdir way,
-	std::ios::openmode which)
-#endif
 {
 	if(!mBuffer
 	   || ((way == std::ios::beg) && (off < 0))
@@ -318,12 +311,8 @@ streampos LLBufferStreamBuf::seekoff(
 		}
 	}
 
-#if( LL_WINDOWS || __GNUC__ > 2 )
 	S32 rv = (S32)(intptr_t)address;
 	return (pos_type)rv;
-#else
-	return (streampos)address;
-#endif
 }