Fix the generation of alignment frags in code sections for AArch64.
    
    	PR gas/20364
    	* config/tc-aarch64.c (s_ltorg): Change the mapping state after
    	aligning the frag.
    	(aarch64_init): Treat rs_align frags in code sections as
    	containing code, not data.
    	* testsuite/gas/aarch64/pr20364.s: New test.
    	* testsuite/gas/aarch64/pr20364.d: New test driver.