gcc and gdb bug caused by imacros usage (gdb emits only <command-line>)

[John Dennis]

Heads up to those performing debugging on 3.x

Recently when I was trying to perform symbolic debugging on components
built from the 3.x tree I discovered I was unable to get any source file
information in gdb, it would only emit <command-line> as the source
filename and I could not get gdb to list source, show it in a backtrace,
etc.

Thanks to Nalin Dahyabhai who discovered the root cause, it's covered in
this bugzilla.

https://bugzilla.redhat.com/show_bug.cgi?id=1004526

Apparently using -imacros causes the failure. To be honest I wasn't all
that familiar with -imacros myself. The workaround I came up with was to
replace -imacros in Make.inc.in with -include.

I don't know which version of the gcc/gdb tool chain this shows up in or
if it's specific to how debuginfo packages are produced during the RPM
build process.

But if you do hit this issue you'll discover it's almost impossible to
do any useful debugging, so heads up, HTH

-- 
John