Avoid redefinition of strcasecmp under mingw-w64

[mjwoods]

Fixes #2083

NetCDF defines strcasecmp as a preprocessor macro on Windows platforms. This is probably needed for the Microsoft compilers, but the header files used by mingw-w64 compilers define strcasecmp as an inline function.

If both the inline function and the macro definitions are used with gcc at high optimisation levels (specifically the flag -foptimize-sibling-calls, which is included by default at -O2 or higher), the OpenDAP tests hang.

On mingw-w64, the macro __MINGW32__ is defined in both 32-bit and 64-bit environments. If this macro is defined, the macro definition of strcasecmp can be disabled, which avoids the hang when running OpenDAP tests.

[mjwoods]

This PR was replaced by #2106 , which is based on a more recent branch .