Fix a crash in compile_to_object function

[libor.bukata@oracle.com]

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On non-Linux platforms, gdb crashes when compile command is issued
because of the null pointer in struct osabi_names gdb_osab. The attached
patch adds a check to avoid this crash and adds osabi name for Solaris.
However, there is probably more work required to enable compile feature
on Solaris (e.g., solaris_infcall_munmap) and other platforms.

Thanks,
Libor

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The patch fixes the crash on non-Linux platforms when
os_rx is a null pointer and converted to C++ std::string.

--- gdb-8.3/gdb/osabi.c	2019-08-19 11:15:04.176948730 +0000
+++ gdb-8.3/gdb/osabi.c	2019-08-19 11:13:43.202284584 +0000
@@ -63,7 +63,7 @@ static const struct osabi_names gdb_osab
 
   { "SVR4", NULL },
   { "GNU/Hurd", NULL },
-  { "Solaris", NULL },
+  { "Solaris", "solaris[2-9]\.[0-9][0-9]" },
   { "GNU/Linux", "linux(-gnu[^-]*)?" },
   { "FreeBSD", NULL },
   { "NetBSD", NULL },
--- gdb-8.3/gdb/compile/compile.c	2019-08-19 13:07:57.669785758 +0000
+++ gdb-8.3/gdb/compile/compile.c	2019-08-19 13:07:33.865626973 +0000
@@ -697,7 +697,7 @@ compile_to_object (struct command_line *
       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) + "(-[^-]*)?-" + (os_rx ? : "");
       compiler->set_triplet_regexp (triplet_rx.c_str ());
     }