[gdb/testsuite] Handle precise-aligned-alloc.c for remote host

With test-case gdb.arch/i386-sse.exp (and likewise gdb.arch/i386-avx.exp) and
host board local-remote-host-notty and target board native-gdbserver I run
into:
...
gdb compile failed, i386-sse.c:68:10: fatal error: \
  ../lib/precise-aligned-alloc.c: No such file or directory
 #include "../lib/precise-aligned-alloc.c"
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...

Fix this using '#include "precise-aligned-alloc.c"' and making that work with
non-remote and remote host.

Tested on x86_64-linux.