Fix up -Wliteral-suffix warning on mti-linux.h

Fix up -Wliteral-suffix warning on mti-linux.h

I've noticed while trying to reproduce PR92989 the following warning:
In file included from ./tm.h:42,
                 from ../../gcc/backend.h:28,
                 from ../../gcc/lra-assigns.c:80:
../../gcc/config/mips/mti-linux.h:31:5: warning: invalid suffix on literal; C++11 requires a space between literal and string macro [-Wliteral-suffix]
     "/%{mmicromips:micro}mips%{mel|EL:el}-"MIPS_SYSVERSION_SPEC  \
     ^
This fixes it, string concatenation works just fine even with whitespace
in between.

2020-04-02  Jakub Jelinek  <jakub@redhat.com>

	* config/mips/mti-linux.h (SYSROOT_SUFFIX_SPEC): Add a space in
	between a string literal and MIPS_SYSVERSION_SPEC macro.