gcc: reconfigure build system

Split from #371092.

See <https://github.com/NixOS/nixpkgs/pull/371092/files#r2401287986> and
<https://wiki.debian.org/Autoreconf> for some rationale.

Co-Authored-By: Arsen Arsenović <arsen@aarsen.me>

pkgs/development/compilers/gcc/common/dependencies.nix

@@ -7,6 +7,7 @@
   texinfo,
   which,
   gettext,
+  autoconf269,
   gnused,
   patchelf,
   gmp,
@@ -41,6 +42,7 @@ in
     texinfo
     which
     gettext
+    autoconf269
   ]
   ++ optionals (perl != null) [ perl ]
   ++ optionals (with stdenv.targetPlatform; isVc4 || isRedox || isSnapshot && flex != null) [ flex ]

pkgs/development/compilers/gcc/common/pre-configure.nix

@@ -80,6 +80,19 @@ lib.optionalString (hostPlatform.isSunOS && hostPlatform.is64bit) ''
       export inhibit_libc=true
     ''
 
+# We need to reconfigure the build system in case it has been patched. Since
+# gcc is patched quite often, reconfiguring it unconditionally makes sense.
+# This is also good practice for a couple other reasons.
+# See <https://wiki.debian.org/Autoreconf>.
++ ''
+  for i in */configure.ac; do
+    pushd "$(dirname "$i")"
+    echo "Running autoreconf in $PWD"
+    autoconf -f
+    popd
+  done
+''
+
 + lib.optionalString (
   (!lib.systems.equals targetPlatform hostPlatform) && withoutTargetLibc && enableShared
 ) (import ./libgcc-buildstuff.nix { inherit lib stdenv; })

pkgs/development/compilers/gcc/default.nix

@@ -30,6 +30,7 @@
   which,
   patchelf,
   binutils,
+  autoconf269,
   isl ? null, # optional, for the Graphite optimization framework.
   zlib ? null,
   libucontext ? null,
@@ -131,6 +132,7 @@ let
     # inherit generated with 'nix eval --json --impure --expr "with import ./. {}; lib.attrNames (lib.functionArgs gcc${majorVersion}.cc.override)" | jq '.[]' --raw-output'
     inherit
       apple-sdk
+      autoconf269
       binutils
       buildPackages
       cargo