glib-private: fix build under Cygwin
fb58d551 added weak linking for ASAN, skipping it for MinGW because weak symbols are broken there. The same is true for Cygwin, so skip things there too.
This fixes the following build error under MSYS2:
/usr/lib/gcc/x86_64-pc-msys/13.3.0/../../../../x86_64-pc-msys/bin/ld: glib/msys-glib-2.0-0.dll.p/gutils.c.o:gutils.c: (.rdata$.refptr.__lsan_enable[.refptr.__lsan_enable]+0x0): undefined reference to `__lsan_enable'