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/llnamevalue.cpp

@@ -168,7 +168,7 @@ void LLNameValue::init(const char *name, const char *data, const char *type, con
 		}
 
 		// finite checks
-		if (!llfinite(t1) || !llfinite(t2) || !llfinite(t3))
+		if (!std::isfinite(t1) || !std::isfinite(t2) || !std::isfinite(t3))
 		{
 			t1 = 0.f;
 			t2 = 0.f;