utils/genrandconfig: disable libopenssl without atomics

libopenssl needs atomic or the build will fail (e.g. on sparcv8 without
libatomic):

${LDCMD:-/nvmedata/autobuild/instance-7/output-1/host/bin/sparc-buildroot-linux-uclibc-gcc}  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -O0 -g2  -g2  -L.   \
	-o apps/openssl apps/asn1pars.o apps/ca.o apps/ciphers.o apps/cms.o apps/crl.o apps/crl2p7.o apps/dgst.o apps/dhparam.o apps/dsa.o apps/dsaparam.o apps/ec.o apps/ecparam.o apps/enc.o apps/engine.o apps/errstr.o apps/gendsa.o apps/genpkey.o apps/genrsa.o apps/nseq.o apps/ocsp.o apps/openssl.o apps/passwd.o apps/pkcs12.o apps/pkcs7.o apps/pkcs8.o apps/pkey.o apps/pkeyparam.o apps/pkeyutl.o apps/prime.o apps/rand.o apps/rehash.o apps/req.o apps/rsa.o apps/rsautl.o apps/s_client.o apps/s_server.o apps/s_time.o apps/sess_id.o apps/smime.o apps/speed.o apps/spkac.o apps/srp.o apps/storeutl.o apps/ts.o apps/verify.o apps/version.o apps/x509.o \
	 apps/libapps.a -lssl -lcrypto -ldl
/nvmedata/autobuild/instance-7/output-1/host/lib/gcc/sparc-buildroot-linux-uclibc/10.3.0/../../../../sparc-buildroot-linux-uclibc/bin/ld: ./libssl.so: undefined reference to `__atomic_fetch_sub_4'

It should be noted that openssl3 has added OPENSSL_DEV_NO_ATOMICS but
"this is intended for internal development only, to check the
refcounting is properly coded.  It should never become a configuration
option, hence the name of the macro.":
https://github.com/openssl/openssl/commit/503d4745a115b82db01c1fb22baaddb153d27cdb

Atomics are not available in Buildroot if:
 - architecture is 32 bit and something other than ARM or xtensa, and
 - GCC < 4.8 or no threads or FLAT.

The nothreads case can theoretically happen in many different
situations, but in practice nobody disables threads. So the only
interesting case is the FLAT case. Since ARM and RISC-V 64 both have
atomics intrinsics, that leaves just m68k NOMMU as FLAT. So this is
truly a corner case.

The proper solution would be to patch GCC to also provide libatomic in
those cases.
- For nothreads, atomics are in fact not needed, so libatomic can simply
  be implemented as stubs.
- For FLAT, it's probably just a matter of having a match to uclinux in
  libatomic/configure.tgt.

Again, though, this happens only in such niche cases that it's not worth
working on it.

Fixes:
 - http://autobuild.buildroot.org/results/bce526d538f43a541fdfbc0c9b4a7cecebbbc539

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle <arnout@mind.be>

utils/genrandconfig

@@ -247,6 +247,11 @@ def fixup_config(sysinfo, configfile):
     if 'BR2_ARM_CPU_ARMV7M=y\n' in configlines and \
        'BR2_PACKAGE_LIBFFI=y\n' in configlines:
         return False
+    # libopenssl needs atomic, but propagating this dependency in
+    # Buildroot is really too much work, so we handle this here.
+    if 'BR2_PACKAGE_LIBOPENSSL=y\n' in configlines and \
+       not 'BR2_TOOLCHAIN_HAS_ATOMIC=y\n' in configlines:
+        return False
     if 'BR2_PACKAGE_SUNXI_BOARDS=y\n' in configlines:
         configlines.remove('BR2_PACKAGE_SUNXI_BOARDS_FEX_FILE=""\n')
         configlines.append('BR2_PACKAGE_SUNXI_BOARDS_FEX_FILE="a10/hackberry.fex"\n')