GLM 0.9.8.4

Fixes:

• Fixed GTC_packing test failing on GCC x86 due to denorms #212 #577
• Fixed POPCNT optimization build in Clang #512
• Fixed intersectRayPlane returns true in parallel case #578
• Fixed GCC 6.2 compiler warnings #580
• Fixed GTX_matrix_decompose decompose #582 #448
• Fixed GCC 4.5 and older build #566
• Fixed Visual C++ internal error when declaring a global vec type with siwzzle expression enabled #594
• Fixed GLM_FORCE_CXX11 with Clang and libstlc++ which wasn't using C++11 STL features. #604