libmudflap installs it's mf-runtime.h include directly into $prefix/include.
This is the only include file provided by GCC that does that, all other include
files are properly put into a version-specific (sub)directory.
Failure to do so, as in this case, will result in problems when one wants to
install various versions of GCC into the same $prefix.
Frank, would you mind having a look at this?
This has been fixed for GCC 4.2.0, I believe by the following patch:
2006-06-21 Frank Ch. Eigler <email@example.com>
mf-runtime.h installation based on ssp patch for PR 26473 from
Mark Mitchell <firstname.lastname@example.org>.
* configure.ac (ACX_NONCANONICAL_TARGET): Use it.
* Makefile.am (target_noncanonical): Define.
(libsubincludedir): New variable.
(nobase_libsubinclude_HEADERS): Add mf-runtime.h.
* configure, aclocal.m4, config.h.in: Regenerated.
* Makefile.in, testsuite/Makefile.in: Likewise.
* mf-runtime.h: Add #ifndef protection for conflicting _REENTRANT
and _THREAD_SAFE redefinition values.
Thus marking as fixed, after all those years.