Add support for leaf2 and leaf4 on Intel's x86 arch (#80)

* Add support for leaf4 on Intel's x86 arch
* Update cpuinfo_x86.h
* Fix typo
* Force compiler to use C99
* Add Intel x86 leaf2 support
* Fixes after review
* Fix review comments
diff --git a/CMakeLists.txt b/CMakeLists.txt
index c8ab9ec..4954805 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -2,6 +2,8 @@
 
 project(CpuFeatures VERSION 0.1.0)
 
+set(CMAKE_C_STANDARD 99)
+
 # Default Build Type to be Release
 if(NOT CMAKE_BUILD_TYPE)
   set(CMAKE_BUILD_TYPE "Release" CACHE STRING