Hello!

I discovered that 'icu4c' failed to build for x86_64 on 'core-updates'.
After some investigation, it turns out to be a problem with <math.h> in
C++ mode, due to its usage of C-only builtins (in the 2.26 release).

Here are the relevant bug reports I've found so far by digging through
the "release/2.26/master" branch, aka "2.26 stable"[0]:

<https://sourceware.org/bugzilla/show_bug.cgi?id=21930>
<https://sourceware.org/bugzilla/show_bug.cgi?id=22235>
<https://sourceware.org/bugzilla/show_bug.cgi?id=22146>
<https://sourceware.org/bugzilla/show_bug.cgi?id=22296>

The attached patch includes the fixes from those bugs, as well as a
couple of others that looked important.  However it's still a very small
subset of the 2.26 post-release fixes.

I've read through _most_ of the commits and around half of them look
important enough to pick "unconditionally".  The other half I mainly
lack the context or skills to assess.

So I wonder if we should simply pick everything from this branch,
instead of only the few that fixes immediately visible problems.
Thoughts?

[0] https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/release/2.26/master