Add a new property of the shader backend which indicates whether the
shader backend is able to dirtify single constants rather than
dirtifying vshader and pshader constants as a whole. Depending on this
a different Set*ConstantF implementation is used which marks constants
dirty. The ARB shader backend uses this and marks constants clean
after uploading.

libport: Undefine strcasecmp and strncasecmp in case they are defined to stricmp and strnicmp respectively.

Define these to _strtoi64 and _strtoui64 if these are available instead.