Fix use of ARM ADR and ADRl pseudo-instructions with thumb function symbols.

	PR gas/21458
	* config/tc-arm.c (do_adr): If the ADR involves a thumb function
	symbol, ensure that the T bit will be set.
	(do_adrl): Likewise.
	(do_t_adr): Likewise.
	* testsuite/gas/arm/pr21458.s: New test.
	* testsuite/gas/arm/pr21458.d: New test driver.