Get the Gnutls code compiling on Fedora 30

The recent changes caused the build to fail on Fedora 30 when built
with --enable-gcc-warnings, among other things with diagnostics that
gnutls_compression_get and gnutls_compression_get_name are deprecated
(this started with GnuTLS 3.6).  Fix this by refusing to call these
obsolescent and now-dummy functions in GnuTLS 3.6 and later.  However,
this is just a temporary workaround to get the build working; a real
fix is needed, as network-stream-tests fail.
* src/gnutls.c (HAVE_GNUTLS_COMPRESSION_GET): New macro.
(gnutls_compression_get, gnutls_compression_get_name):
Define only if HAVE_GNUTLS_COMPRESSION_GET.
(init_gnutls_functions): Load the two functions only if
HAVE_GNUTLS_COMPRESSION_GET.
(emacs_gnutls_certificate_export_pem): Use alloca instead of xmalloc.
(Fgnutls_peer_status): Just return "NULL" if the functions
are deprecated.
(Fgnutls_format_certificate): Fix pointer signedness glitches.
* src/process.c: Fix spacing.
1 job for master in 7 minutes and 10 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
failed #3099
test-all

00:07:10

 
Name Stage Failure
failed
test-all Test
make[2]: *** [xdisp.o] Error 1
Makefile:402: recipe for target 'xdisp.o' failed
make[2]: Leaving directory '/builds/emacs/emacs/src'
Makefile:424: recipe for target 'src' failed
make[1]: *** [src] Error 2
make[1]: Leaving directory '/builds/emacs/emacs'
Makefile:1117: recipe for target 'bootstrap' failed
make: *** [bootstrap] Error 2
ERROR: Job failed: exit code 1