Build problems with glibc 2.26

[Rolf Eike Beer]

Hi,

I'm trying to build gcc 5.4.0 together with glibc 2.26. It is a cross-build to 
both AMD64 or i686 that shows problems, while ARM works. (For those who want 
to suggest a newer gcc first: no, doesn't work: https://gcc.gnu.org/bugzilla/
show_bug.cgi?id=70936).

The problem arises from this output of configure of libgomp:

checking for ISO C99 support in <math.h>... no

This has always been "yes" before. This leads to I-don't-know-which-changes, 
which leads to std::to_string not being available (and probably some related 
problems), which afterwards will lead to gdb 8.0 not being able to be 
(cross-)compiled.

My initial idea was this:

echo 'glibcxx_cv_c99_math=yes' >> ${CONFIG_SITE}
export CONFIG_SITE

Which would be ok, if not most sub-configures are called with

  CONFIG_SITE=no-such-file

Why is this? I have just removed all of them an the only difference I was able 
to observe is that now the CONFIG_SITE workaround work, while all other 
results are the same. Looking in the git history this seems to be the case 
forever, but I would propose for this to be reconsidered.

Greetings,

Eike
-- 
Rolf Eike Beer, emlix GmbH, http://www.emlix.com
Fon +49 551 30664-0, Fax +49 551 30664-11
Bertha-von-Suttner-Str. 9, 37085 Göttingen, Germany
Sitz der Gesellschaft: Göttingen, Amtsgericht Göttingen HR B 3160
Geschäftsführung: Heike Jordan, Dr. Uwe Kracke – Ust-IdNr.: DE 205 198 055

emlix – smart embedded open source
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