Update minimum g++ version in documentation

Version changed due to a newer requirement in LLVM.

README.md

@@ -20,7 +20,7 @@ documentation.
 ## Building from Source
 
 1. Make sure you have installed the dependencies:
-    * `g++` 4.4 or `clang++` 3.x
+    * `g++` 4.7 or `clang++` 3.x
     * `python` 2.6 or later (but not 3.x)
     * `perl` 5.0 or later
     * GNU `make` 3.81 or later

src/doc/tutorial.md

@@ -90,7 +90,7 @@ supported build environments that are most likely to work.
 To build from source you will also need the following prerequisite
 packages:
 
-* g++ 4.4 or clang++ 3.x
+* g++ 4.7 or clang++ 3.x
 * python 2.6 or later (but not 3.x)
 * perl 5.0 or later
 * gnu make 3.81 or later