MIPS/GAS/testsuite: Disable compact EH #7 tests with OpenBSD targets

MIPS/GAS/testsuite: Disable compact EH #7 tests with OpenBSD targets

Compact EH #7 tests use output templates that are not suitable for the
n64 ABI, which `mips64*-*-openbsd*' targets use by default, because the
contents of the sections examined are expected to be differnt.  Disable
the tests then, removing these regressions:

mips64-openbsd  -FAIL: Compact EH EB #7 with personality id and fallback FDE
mips64-openbsd  -FAIL: Compact EH EL #7 with personality id and fallback FDE
mips64el-openbsd  -FAIL: Compact EH EB #7 with personality id and fallback FDE
mips64el-openbsd  -FAIL: Compact EH EL #7 with personality id and fallback FDE

Suitable corresponding tests for the n64 ABI can be added separately.

	gas/
	* testsuite/gas/mips/compact-eh-eb-7.d: Exclude for
	`mips64*-*-openbsd*'.
	* testsuite/gas/mips/compact-eh-el-7.d: Likewise.