Trouble building with -DDEBUG_MANGLE

[Cooper, Karl (US SSA)]

...gcc/cp/mangle.c mentions DEBUG_MANGLE.  Since I'm trying to figure
out how gcc 4.2.3 is mangling thunk names, I thought I'd build gcc 4.2.3
with that macro turned on:

make BOOT_CFLAGS="-DDEBUG_MANGLE" bootstrap

...but this does not succeed; the build fails with an internal compiler
error caused by a segmentation fault.

Does anyone have any experience building a relatively recent gcc with
DEBUG_MANGLE turned on?