tweak debug mingw opt level and updated msvc version used in env_windows.yxy to Visual Studio Community Edition 2017 15.6.2

bin/env_windows.txt

@@ -33,12 +33,12 @@ MX2_LD_OPTS_WINDOWS_RELEASE=
 
 'C Compiler options. Note: -D_WIN32_WINNT=0x0601 means headers for Windows 7, ie: Windows 7 is min SDK!
 MX2_CC_OPTS_WINDOWS=-std=gnu99 -D_WIN32_WINNT=0x0603 -m32
-MX2_CC_OPTS_WINDOWS_DEBUG=-Os
+MX2_CC_OPTS_WINDOWS_DEBUG=-O2
 MX2_CC_OPTS_WINDOWS_RELEASE=-O3 -DNDEBUG
 
 'C++ Compiler options
 MX2_CPP_OPTS_WINDOWS=-std=c++11 -D_WIN32_WINNT=0x0603 -m32
-MX2_CPP_OPTS_WINDOWS_DEBUG=-Os
+MX2_CPP_OPTS_WINDOWS_DEBUG=-O2
 MX2_CPP_OPTS_WINDOWS_RELEASE=-O3 -DNDEBUG
 
 '***** WINDOWS DESKTOP TARGET - MSVC *****
@@ -46,7 +46,8 @@ MX2_CPP_OPTS_WINDOWS_RELEASE=-O3 -DNDEBUG
 'directories
 MX2_MSVC_DIR=${ProgramFiles(x86)}\Microsoft Visual Studio\2017\Community\VC
 
-MX2_MSVC_TOOLS_DIR=${MX2_MSVC_DIR}\Tools\MSVC\14.12.25827
+'For Visual Studio Community Edition 2017 15.6.2
+MX2_MSVC_TOOLS_DIR=${MX2_MSVC_DIR}\Tools\MSVC\14.13.26128
 
 MX2_WINDOWS_KITS_DIR=${ProgramFiles(x86)}\Windows Kits\10