PR gas/20429
* config/tc-arm.c (do_vfp_nsyn_push): Check that no more than 16
registers are pushed.
(do_vfp_nsyn_pop): Check that no more than 16 registers are
popped.
* testsuite/gas/arm/pr20429.s: New test.
* testsuite/gas/arm/pr20429.d: New test driver.
* testsuite/gas/arm/pr20429.1: Expected error output.