Handle internal functions in is_tm_pure_call

Handle internal functions in is_tm_pure_call

The upcoming changes to use internal functions for things like sqrt
caused a failure in gcc.dg/tm/20100610.c, because we were trying to get
call flags from the null gimple_call_fn of an IFN_SQRT call.  We've been
making fairly heavy use of internal functions for a while now so I think
this might be latent.

Tested on x86_64-linux-gnu, aarch64-linux-gnu and arm-linux-gnueabi.

gcc/
	* trans-mem.c (is_tm_pure_call): Use gimple_call_flags for
	internal functions.

From-SVN: r229925