Avoid generating *UND* symbols in object files

Avoid generating *UND* symbols in object files

The swint-emulation test contains hand-generated asm stubs which use arbitrary
identifiers just for their mnemonic properties.  Unfortunately, their use in
the .if statements generate *UND* symbols listed in the object files export
table.

Use .ifc rather than .if, which explicit interprets its parameters as strings
rather than expressions.  Unfortunately, there is no .elseifc directive.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>