fedora-34: add gmp-devel

Fixes:
46.99 swtpm_localca.c:27:10: fatal error: gmp.h: No such file or directory
46.99    27 | #include <gmp.h>
46.99       |          ^~~~~~~

Signed-off-by: Bill Roberts <bill.c.roberts+gh@gmail.com>

fedora-34.docker.m4

@@ -64,7 +64,8 @@ RUN dnf -y install \
     json-glib-devel \
     libusb-devel \
     libftdi-devel \
-    python3-devel
+    python3-devel \
+    gmp-devel
 
 include(`pip3.m4')
 include(`autoconf.m4')