Remove a bunch of usages of gdb_suppress_tests in 'runto_main'.

Remove a bunch of usages of gdb_suppress_tests in 'runto_main'.

In the 'info -q -t' patch series, I started a new test from
gdb.threads/threadapply.exp, that uses an obsolete way to do
runto_main.

This patch changes all occurrences of runto_main using gdb_suppress_tests
to use instead fail+return.

Note that there are still about 220 occurrences of gdb_suppress_tests
but unclear (to me) if these can be similarly trivially be replaced by a
fail+return.  Further cleanup can be done in follow-up patches.

Tests run on Debian/x86_64.

gdb/testsuite/ChangeLog
2018-10-27  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

	* gdb.arch/altivec-regs.exp: Do not use gdb_suppress_tests in
	runto_main, use fail + return instead.
	gdb.arch/amd64-byte.exp: Likewise.
	gdb.arch/amd64-dword.exp: Likewise.
	gdb.arch/amd64-word.exp: Likewise.
	gdb.arch/e500-abi.exp: Likewise.
	gdb.arch/e500-regs.exp: Likewise.
	gdb.arch/gdb1291.exp: Likewise.
	gdb.arch/gdb1431.exp: Likewise.
	gdb.arch/i386-avx.exp: Likewise.
	gdb.arch/i386-byte.exp: Likewise.
	gdb.arch/i386-prologue.exp: Likewise.
	gdb.arch/i386-sse.exp: Likewise.
	gdb.arch/i386-word.exp: Likewise.
	gdb.arch/iwmmxt-regs.exp: Likewise.
	gdb.arch/pa-nullify.exp: Likewise.
	gdb.arch/powerpc-prologue.exp: Likewise.
	gdb.arch/s390-tdbregs.exp: Likewise.
	gdb.arch/vsx-regs.exp: Likewise.
	gdb.asm/asm-source.exp: Likewise.
	gdb.base/auxv.exp: Likewise.
	gdb.base/bigcore.exp: Likewise.
	gdb.base/overlays.exp: Likewise.
	gdb.base/savedregs.exp: Likewise.
	gdb.base/setshow.exp: Likewise.
	gdb.base/sigaltstack.exp: Likewise.
	gdb.base/sigbpt.exp: Likewise.
	gdb.base/siginfo-addr.exp: Likewise.
	gdb.base/siginfo-obj.exp: Likewise.
	gdb.base/siginfo-thread.exp: Likewise.
	gdb.base/siginfo.exp: Likewise.
	gdb.base/signull.exp: Likewise.
	gdb.base/sigrepeat.exp: Likewise.
	gdb.base/structs2.exp: Likewise.
	gdb.threads/threadapply.exp: Likewise.
	gdb.threads/watchthreads.exp: Likewise.
	gdb.threads/watchthreads2.exp: Likewise.