I think I understand at least part of the problem:
(1) I configure gcc with
../work/configure --prefix=/opt/gcc/gcc4.8w
--enable-languages=c,c++,fortran,objc,obj-c++,java,ada,lto --with-gmp=/opt/mp
--with-system-zlib --with-isl=/opt/mp --enable-lto --enable-plugin
--enable-build-with-cxx
i.e., the files for gmp, mpfr, mpc, isl, ... are found in /opt/mp
(2) before r194665 the files including gcc/system.h did not need gmp.h
and the tests using it in configure were happy with
gcc -c -g -I../../work/gcc -I../../work/gcc/../include conftest.c >&5
(3) starting with r194665 all these tests fails as
configure:10333: checking whether getenv is declared
configure:10356: gcc -c -g -I../../p_work/gcc -I../../p_work/gcc/../include
conftest.c >&5
In file included from conftest.c:108:0:
../../p_work/gcc/system.h:641:17: fatal error: gmp.h: No such file or directory
#include <gmp.h>
^
compilation terminated.
configure:10356: $? = 1
I think the fix requires to use gmpinc='-I/opt/mp/include '
Dominique
