[pushed] Avoid crash in compile_to_object

[pushed] Avoid crash in compile_to_object

[Tom Tromey]

PR 23672 points out a crash in compile_to_object.  This crash came in
during a C++-ization.  This patch avoids the crash.

The PR also points out another weird behavior in this code, but that
one requires some setup that I don't have here, and it seems to date
back to the introduction of the compile feature.  So, it isn't
addressed here.  I will leave the PR open so this bug isn't forgotten.

gdb/ChangeLog
2021-01-09  Tom Tromey  <tom@tromey.com>

	PR compile/23672
	* compile/compile.c (compile_to_object): Avoid crash when
	osabi_triplet_regexp returns NULL.
---
 gdb/ChangeLog         | 6 ++++++
 gdb/compile/compile.c | 4 +++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/gdb/compile/compile.c b/gdb/compile/compile.c
index d4c0034452d..074a865f9cc 100644
--- a/gdb/compile/compile.c
+++ b/gdb/compile/compile.c
@@ -703,7 +703,9 @@ compile_to_object (struct command_line *cmd, const char *cmd_string,
       const char *arch_rx = gdbarch_gnu_triplet_regexp (gdbarch);
 
       /* Allow triplets with or without vendor set.  */
-      triplet_rx = std::string (arch_rx) + "(-[^-]*)?-" + os_rx;
+      triplet_rx = std::string (arch_rx) + "(-[^-]*)?-";
+      if (os_rx != nullptr)
+	triplet_rx += os_rx;
       compiler->set_triplet_regexp (triplet_rx.c_str ());
     }
 
-- 
2.26.2