[Bug bootstrap/51935] New: Configure fails on included mpc/mpfr

["psmith at gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51935

             Bug #: 51935
           Summary: Configure fails on included mpc/mpfr
    Classification: Unclassified
           Product: gcc
           Version: 4.6.2
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: bootstrap
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: psmith@gnu.org


Created attachment 26404
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26404
Add /src to mpfr directories in configure.ac

I was trying to follow the advice of various people by including GMP/MPC/MPFR
into the GCC source tree (GCC 4.6.2 / GMP 5.0.2 / MPFR 3.1.0 / MPC 0.9),
however this failed during configure:

    checking whether time.h and sys/time.h may both be included... yes
    checking for creal in -lm... yes
    checking for __gmpz_init in -lgmp... yes
    checking for MPFR... yes
    checking for recent GMP... yes
    checking for recent MPFR... no
    configure: error: MPFR version >= 2.4.2 required
    make[4]: *** [configure-stage1-mpc] Error 1
    make[4]: Leaving directory `/usr/src/gcc/obj-stage1/gcc'
    make[3]: *** [stage1-bubble] Error 2
    make[3]: Leaving directory `/usr/src/gcc/obj-stage1/gcc'
    make[2]: *** [all] Error 2
    make[2]: Leaving directory `/usr/src/gcc/obj-stage1/gcc'
    make[1]: *** [/usr/src/gcc/.stamp/stage1.install] Error 2

Investigating, I found the configure was using the wrong path to location mpfr
headers and libraries; for example mpc/config.log says:

    configure:11278: checking for recent MPFR
    configure:11290: gcc -c -g -fkeep-inline-functions
-I/usr/src/gcc/obj-stage1/gcc
    /./gmp -I/usr/src/gcc/gcc-4.6.2/mpfr  conftest.c >&5
    conftest.c:34:3: error: #error "Minimal MPFR version is 2.4.2"
    conftest.c:35: error: expected '=', ',', ';', 'asm' or '__attribute__' at
end of
     input
    configure:11290: $? = 1

This is due to the configure script assuming that MPFR headers are in the root
MPFR directory, but they're not: they live the "src" subdirectory in MPFR.  If
you fix the headers then it will fail during link because it's looking for
libmpfr.a in the wrong place, too.

I have an MPFR installed natively on the system, but it's version 2.2.1.  My
suspicion is that most people who test this already have a "new enough" MPFR
installed in /usr/include so they don't notice that this path is wrong, since
configure finds the one in /usr/include and is happy with it.

The attached patch to configure.ac that fixes things.