Compile issues with GCC 10 (multiple definition of `verbose')

[robert-scheck]

When trying to build rpki-client on Fedora 33/Rawhide (i686, x86_64, armv7hl, aarch64, ppc64le, s390x) using GCC 10.0.1, it fails like this:

[…]
cc1: warning: unrecognized command-line option '-Wno-incompatible-pointer-types-discards-qualifiers'
cc -o rpki-client main.o as.o cert.o cms.o compats.o crl.o io.o ip.o log.o mft.o output.o output-bird.o output-bgpd.o output-csv.o output-json.o roa.o rsync.o tal.o validate.o x509.o -Wl,-z,relro -Wl,--as-needed  -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld -lssl -lcrypto  -lresolv 
cc -g -W -Wall -Wextra -Wmissing-prototypes -Wstrict-prototypes -Wwrite-strings -Wno-unused-parameter -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection  -Wno-incompatible-pointer-types-discards-qualifiers   -c -o test-cert.o test-cert.c
cc -o test-cert test-cert.o as.o cert.o cms.o compats.o crl.o io.o ip.o log.o mft.o output.o output-bird.o output-bgpd.o output-csv.o output-json.o roa.o rsync.o tal.o validate.o x509.o -Wl,-z,relro -Wl,--as-needed  -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld -lssl -lcrypto  -lresolv 
/usr/bin/ld: log.o:(.bss+0x0): multiple definition of `verbose'; test-cert.o:/builddir/build/BUILD/rpki-client-VERSION_0_3_0/extern.h:263: first defined here
collect2: error: ld returned 1 exit status
make: *** [Makefile:96: test-cert] Error 1

Building using GCC 9.2.1 succeeds on the same architectures, thus it feels like this is https://gcc.gnu.org/gcc-10/porting_to.html (default to -fno-common).