S12Z: gas: Fix bug when a symbol name was the single letter 'c'.
The assembler incorrectly recognised "c" as a register name, and refused to allow it where it expected a symbol/label. gas/ * config/tc-s12z.c (lex_reg_name): Compare the length of the strings before the contents. * testsuite/gas/s12z/labels.d: New file. * testsuite/gas/s12z/labels.s: New file. * testsuite/gas/s12z/s12z.exp: Add them.