[Bug bootstrap/67728] Build fails when cross-compiling with in-tree GMP and ISL

["bernd.edlinger at hotmail dot de" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67728

--- Comment #26 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
with unpatched trunk and mpfr-3.1.4 and mpc-1.0.3 in-tree

I've got this in mpc/src/libmpc.la:
dependency_libs=' -lmpfr /home/ed/gnu/gcc-build1/./gmp/.libs/libgmp.la -lm'

and check-mpc fails to build this:
libtool: link: /home/ed/gnu/gcc-build1/./prev-gcc/xgcc
-B/home/ed/gnu/gcc-build1/./prev-gcc/
-B/home/ed/gnu/install1/x86_64-pc-linux-gnu/bin/
-B/home/ed/gnu/install1/x86_64-pc-linux-gnu/bin/
-B/home/ed/gnu/install1/x86_64-pc-linux-gnu/lib/ -isystem
/home/ed/gnu/install1/x86_64-pc-linux-gnu/include -isystem
/home/ed/gnu/install1/x86_64-pc-linux-gnu/sys-include -g -O2 -static-libstdc++
-static-libgcc -o tabs tabs.o  ./.libs/libmpc-tests.a ../src/.libs/libmpc.a
-lmpfr /home/ed/gnu/gcc-build1/./gmp/.libs/libgmp.a -lm
/usr/bin/ld: cannot find -lmpfr

and with the patch this line in mpc/src/libmpc.la changed to:
dependency_libs=' /home/ed/gnu/gcc-build/./mpfr/.libs/libmpfr.la
/home/ed/gnu/gcc-build/./gmp/.libs/libgmp.la'

and the check-mpc succeeds on a plain x86_64-ubuntu14.04 with definitely no
gmp or mpfr libs installed