For SYSTEM linux-mingw32 and linux-mingw64 default GLEW_DEST more appropriately

[nigels-com]

For Issue #316

$ sudo make SYSTEM=linux-mingw32 install
install -d -m 0755 "/usr/local/i686-w64-mingw32/include/GL"
install -m 0644 include/GL/wglew.h "/usr/local/i686-w64-mingw32/include/GL/"
install -m 0644 include/GL/glew.h "/usr/local/i686-w64-mingw32/include/GL/"
install -m 0644 include/GL/glxew.h "/usr/local/i686-w64-mingw32/include/GL/"
install -m 0644 include/GL/eglew.h "/usr/local/i686-w64-mingw32/include/GL/"
sed \
	-e "s|@prefix@|/usr/local|g" \
	-e "s|@libdir@|/usr/local/i686-w64-mingw32/lib|g" \
	-e "s|@exec_prefix@|/usr/local/i686-w64-mingw32/bin|g" \
	-e "s|@includedir@|/usr/local/i686-w64-mingw32/include/GL|g" \
	-e "s|@version@|2.2.0|g" \
	-e "s|@cflags@||g" \
	-e "s|@libname@|glew32|g" \
	-e "s|@libgl@|-L/usr/i686-w64-mingw32/lib -lopengl32 -lgdi32 -luser32 -lkernel32|g" \
	-e "s|@requireslib@|glu|g" \
	< glew.pc.in > glew.pc
install -d -m 0755 "/usr/local/i686-w64-mingw32/lib"
install -m 0644 lib/glew32.dll "/usr/local/i686-w64-mingw32/lib/"
install -m 0644 lib/libglew32.a         "/usr/local/i686-w64-mingw32/lib/"
install -d -m 0755 "/usr/local/i686-w64-mingw32/lib/pkgconfig"
install -d -m 0755 "/usr/local/i686-w64-mingw32/lib/pkgconfig"
install -m 0644 glew.pc "/usr/local/i686-w64-mingw32/lib/pkgconfig/"

$ find /usr/local/i686-w64-mingw32/
/usr/local/i686-w64-mingw32/
/usr/local/i686-w64-mingw32/lib
/usr/local/i686-w64-mingw32/lib/libglew32.a
/usr/local/i686-w64-mingw32/lib/pkgconfig
/usr/local/i686-w64-mingw32/lib/pkgconfig/glew.pc
/usr/local/i686-w64-mingw32/lib/glew32.dll
/usr/local/i686-w64-mingw32/include
/usr/local/i686-w64-mingw32/include/GL
/usr/local/i686-w64-mingw32/include/GL/wglew.h
/usr/local/i686-w64-mingw32/include/GL/glxew.h
/usr/local/i686-w64-mingw32/include/GL/glew.h
/usr/local/i686-w64-mingw32/include/GL/eglew.h