libcpp: fix ICE comparing macro locations without column info [PR96391]

PR preprocessor/96391 describes an ICE in the C++ frontend on:

  #define CONST const
  #define VOID void
  typedef CONST VOID *PCVOID;

where the typedef line occurs after enough code has been compiled
that location_t values are beyond LINE_MAP_MAX_LOCATION_WITH_COLS,
and hence no column numbers are available.

The issue occurs in linemap_compare_locations when comparing the
locations of the "const" and "void" tokens.
Upon resolving the LRK_MACRO_EXPANSION_POINT, both have the same
location_t, the line of the "typedef" (with no column), and so
the l0 == l1 clause is triggered, but they are not from the
same macro expansion, leading first_map_in_common to return NULL
and triggering the "abort" condition.

This patch fixes the issue by checking when the two macro expansion
point location_t values are equal that the value
<= LINE_MAP_MAX_LOCATION_WITH_COLS and thus has column information,
fixing the issue.

gcc/testsuite/ChangeLog:
	PR preprocessor/96391
	* g++.dg/plugin/location-overflow-test-pr96391.c: New test.
	* g++.dg/plugin/plugin.exp (plugin_test_list): Add it,
	using the location_overflow_plugin.c from gcc.dg/plugin.

libcpp/ChangeLog:
	PR preprocessor/96391
	* line-map.c (linemap_compare_locations): Require that
	the location be <= LINE_MAP_MAX_LOCATION_WITH_COLS when
	treating locations as coming from the same macro expansion.

1 files changed, 2 insertions, 1 deletions

diff --git a/libcpp/line-map.c b/libcpp/line-map.c
index 2432cd5..cccacf2 100644
--- a/libcpp/line-map.c
+++ b/libcpp/line-map.c
@@ -1417,7 +1417,8 @@ linemap_compare_locations (line_maps *set,
 
   if (l0 == l1
       && pre_virtual_p
-      && post_virtual_p)
+      && post_virtual_p
+      && l0 <= LINE_MAP_MAX_LOCATION_WITH_COLS)
     {
       /* So pre and post represent two tokens that are present in a
 	 same macro expansion.  Let's see if the token for pre was