RFC: C/C++ preprocessor macro support for GDB

[Jim Blandy]

Instead of the bug you guessed, here's the bug I actually do have:

(gdb) show macro A
Defined at /home/jimb/gdb/macros/play/test.c:12
#define A(x) x
(gdb) show macro B
Defined at /home/jimb/gdb/macros/play/test.c:12
#define B(x) A
(gdb) macro expand B(ignored)(passed through)
expands to: A(passed through)
(gdb) 

ISO/IEC 9899:1999(E) 6.10.3.4 para 1: "Then, the resulting
preprocessing token sequence is rescanned, along with all subsequent
preprocessing tokens of the source file, for more macro names to
replace."  It's the "along with all subsequent PP tokens" part that I
got wrong.

(Did I mention that I think we should replace macroexp.c with libcpp?)