Silence objtool warnings from 55d7afa4

The use of __noreturn__ in 55d7afa4ad on
spl_panic() caused objtool warnings on Linux when the kernel is built
with CONFIG_STACK_VALIDATION=y. This patch works around that by
restricting the application of __noreturn__ to builds for static
analyzers.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes #14068

include/os/freebsd/spl/sys/debug.h

@@ -54,6 +54,9 @@
 /*
  * Common DEBUG functionality.
  */
+#if defined(__COVERITY__) || defined(__clang_analyzer__)
+__attribute__((__noreturn__))
+#endif
 extern void spl_panic(const char *file, const char *func, int line,
     const char *fmt, ...) __attribute__((__noreturn__));
 extern void spl_dumpstack(void);