gcc: use internal zlib

Commit f355e0af didn't work because
GCC building ignores LDFLAGS when linking libgfortran.so
whereas the latter does not even need zlib and would be linked to
system zlib (if it exists) for nothing.

In our case, there seems to be no zlib code inside the installed files.

component/gcc/buildout.cfg

@@ -8,7 +8,6 @@ extends =
   ../perl/buildout.cfg
   ../tar/buildout.cfg
   ../binutils/buildout.cfg
-  ../zlib/buildout.cfg
 
 parts =
   gcc-8.2
@@ -21,6 +20,8 @@ pre-configure =
   set %(location)s/bin
   mkdir -p $1
   ln -s ${binutils:location}/bin/ld $1/ld
+# remove "dependency_libs=' -lz'" line  (-lz not needed anymore because the internal zlib was used)
+  sed -i '/^libbacktrace\.la:/{ N; s,$,\n\tsed -i /^dependency_libs=/d $@,; }' libbacktrace/Makefile.in
 configure-options =
   --disable-bootstrap
   --disable-multilib
@@ -31,6 +32,7 @@ configure-options =
   --with-isl=${isl:location}
   --with-ld=@@LOCATION@@/bin/ld
   --with-as=${binutils:location}/bin/as
+  --with-internal-zlib
 post-install =
   cd '%(location)s/bin'
   ln -s gcc cc
@@ -51,8 +53,7 @@ post-install =
   EOF
   chmod +x ld
 environment =
-  CPPFLAGS=-I${zlib:location}/include
-  LDFLAGS=-Wl,-rpath=${gmp:location}/lib -Wl,-rpath=${isl:location}/lib -Wl,-rpath=${mpc:location}/lib -Wl,-rpath=${mpfr:location}/lib -L${zlib:location}/lib -Wl,-rpath=${zlib:location}/lib
+  LDFLAGS=-Wl,-rpath=${gmp:location}/lib -Wl,-rpath=${isl:location}/lib -Wl,-rpath=${mpc:location}/lib -Wl,-rpath=${mpfr:location}/lib
   PATH=${binutils:location}/bin:${gettext:location}/bin:${perl:location}/bin:${tar:location}/bin:%(PATH)s
 
 [gcc-5.5]