libc/glibc: configure libc headers with support for 128-bit long double
At the headers install pass, there's no compiler to test for the size
of long double. Help it: we know that the compiler does support 128-bit
long double, in the IBM extended precision.
Kindly pointed out, and explained, by Mike FRYSINGER:
http://sourceware.org/ml/crossgcc/2009-11/msg00040.html
http://sourceware.org/ml/crossgcc/2009-11/msg00057.html