[gdb/testsuite] Fix gdb.base/return-nodebug.exp with local-remote-host.exp

[gdb/testsuite] Fix gdb.base/return-nodebug.exp with local-remote-host.exp

With host board local-remote-host.exp and test-case
gdb.base/return-nodebug.exp, I run into:
...
Executing on host: gcc -fno-stack-protector -fdiagnostics-color=never \
  -DTYPE=signed\ char -c -g  -o return-nodebug-signed-char0.o  \
  /home/vries/gdb_versions/devel/src/gdb/testsuite/gdb.base/return-nodebug.c \
  (timeout = 300)
builtin_spawn [open ...]^M
gcc: error: char: No such file or directory
...

Avoid the quoting problem by not using spaces in the define.

Tested on x86_64-linux.