umip: fix "multiple definition" compilation issue

Fix "multiple definition" compilation issue found in GCC 11.4.1:
cc -no-pie -o umip_test_basic_64 umip_utils_64.o umip_test_basic.c
/usr/bin/ld: /tmp/ccXWxfby.o:(.bss+0xc): multiple definition of `got_signal'; umip_utils_64.o:(.bss+0x8): first defined here
/usr/bin/ld: /tmp/ccXWxfby.o:(.bss+0x10): multiple definition of `got_sigcode'; umip_utils_64.o:(.bss+0xc): first defined here
collect2: error: ld returned 1 exit status

Signed-off-by: Pengfei Xu <[email protected]>

BM/umip/umip_test_basic.c

@@ -35,7 +35,7 @@
 #endif
 
 int test_passed, test_failed, test_errors;
-sig_atomic_t got_signal, got_sigcode;
+extern sig_atomic_t got_signal, got_sigcode;
 
 static void call_sgdt(void)
 {