If a char * global was initialized with a rvalue from
`gcc_jit_context_new_string_literal` containing a format string,
dumping the context causes libgccjit to SIGSEGV due to an improperly
constructed call to vasprintf. The following code snippet can reproduce
the crash:

int main(int argc, char **argv)
{
 gcc_jit_context *ctxt = gcc_jit_context_acquire ();
 gcc_jit_lvalue *var = gcc_jit_context_new_global(
 ctxt, NULL, GCC_JIT_GLOBAL_EXPORTED,
 gcc_jit_context_get_type(ctxt, GCC_JIT_TYPE_CONST_CHAR_PTR),
 "var");
 gcc_jit_global_set_initializer_rvalue(
 var, gcc_jit_context_new_string_literal(ctxt, "%s"));
 gcc_jit_context_dump_to_file (ctxt, "output", 0);
 return 0;
}

The offending line is jit-recording.cc:4922, where a call to d.write
passes the initializer rvalue's debug string to `write` without a
format specifier. The attached patch fixes this issue.

Thanks,
Vibhav
-- 
Vibhav Pant
vibhavp@gmail.com
GPG: 7ED1 D48C 513C A024 BE3A 785F E3FB 28CB 6AB5 9598