egl: Skip closing drivers when building with AddressSanitizer.

egl: Skip closing drivers when building with AddressSanitizer.

If you dlclose your driver, the leak reports look like:

    #0 0xffff9c7e5e7c in malloc (/lib/aarch64-linux-gnu/libasan.so.6+0x9ee7c)
    #1 0xffff94aaaa48  (<unknown module>)
    #2 0xffff94aa5ff4  (<unknown module>)
    #3 0xffff94d1867c  (<unknown module>)
    #4 0xffff94d184f0  (<unknown module>)
    #5 0xffff94c9a990  (<unknown module>)
    #6 0xffff94c92e30  (<unknown module>)
    #7 0xffff94c91d48  (<unknown module>)
    #8 0xffff946eb800  (/home/anholt/src/mesa/build-aarch64-asan/src/egl/libEGL.so.1.0.0+0xfe800)
    #9 0xffff94c72874  (<unknown module>)
    #10 0xffff946ede68  (/home/anholt/src/mesa/build-aarch64-asan/src/egl/libEGL.so.1.0.0+0x100e68)
    #11 0xffff94bf7134  (<unknown module>)
    #12 0xffff9c686450 in dri2_create_screen ../src/egl/drivers/dri2/egl_dri2.c:1079

which is not terribly useful.  Probe if we're building with asan and just
skip closing the driver in the happy path (which seems to be the standard
practice for loadable modules with this tool).

Acked-by: Michel Dänzer <mdaenzer@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7695>