The builtin was accidentally defined to have an integer return value.
Fixed with the attached patch.

gcc/ChangeLog:

2018-06-05  Andreas Krebbel  <krebbel@linux.ibm.com>

	* config/s390/s390-builtin-types.def: Add void function type.
	* config/s390/s390-builtins.def: Use the function type for the
	tbeginc builtin.

gcc/testsuite/ChangeLog:

2018-06-05  Andreas Krebbel  <krebbel@linux.ibm.com>

	* gcc.target/s390/htm-builtins-compile-4.c: New test.

From-SVN: r261183