libcpp: Fix up pragma preprocessing [PR100450]

libcpp: Fix up pragma preprocessing [PR100450]

Since the r0-85991-ga25a8f3be322fe0f838947b679f73d6efc2a412c
https://gcc.gnu.org/legacy-ml/gcc-patches/2008-02/msg01329.html
changes, so that we handle macros inside of pragmas that should expand
macros, during preprocessing we print those pragmas token by token,
with CPP_PRAGMA printed as
      fputs ("#pragma ", print.outf);
      if (space)
        fprintf (print.outf, "%s %s", space, name);
      else
        fprintf (print.outf, "%s", name);
where name is some identifier (so e.g. print
 #pragma omp parallel
or
 #pragma omp for
etc.).  Because it ends in an identifier, we need to handle it like
an identifier (i.e. CPP_NAME) for the decision whether a space needs
to be emitted in between that #pragma whatever or #pragma whatever whatever
and following token, otherwise the attached testcase is preprocessed as
 #pragma omp forreduction(+:red)
rather than
 #pragma omp for reduction(+:red)
The cpp_avoid_paste function is only called for this purpose.

2021-05-07  Jakub Jelinek  <jakub@redhat.com>

	PR c/100450
	* lex.c (cpp_avoid_paste): Handle token1 CPP_PRAGMA like CPP_NAME.

	* c-c++-common/gomp/pr100450.c: New test.

(cherry picked from commit 170c850e4bd46745e2a5130b5eb09f9fceb98416)