i386: fix -march=amd crash

i386: fix -march=amd crash

It started with g:3e2ae3ee285a57455d5a23bd352a68c289130186 where
new entry was added to processor_alias_table after generic node:

+  {"amdfam19h", PROCESSOR_GENERIC, CPU_GENERIC, 0,
+    M_CPU_TYPE (AMDFAM19H), P_NONE},

and then the following is violated:

/* NB: processor_alias_table stops at the "generic" entry.  */

gcc/ChangeLog:

	PR target/99753
	* common/config/i386/i386-common.c (ARRAY_SIZE): Fix off-by-one
	error.
	* config/i386/i386-options.c (ix86_option_override_internal):
	Add run-time assert.

gcc/testsuite/ChangeLog:

	PR target/99753
	* gcc.target/i386/pr99753.c: New test.