gcc: factor out forceLibgccToBuildCrtStuff

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

@@ -3,7 +3,13 @@
 , enableMultilib
 }:
 
+let
+  forceLibgccToBuildCrtStuff =
+    import ./libgcc-buildstuff.nix { inherit lib stdenv; };
+in
+
 originalAttrs: (stdenv.mkDerivation (finalAttrs: originalAttrs // {
+  passthru = (originalAttrs.passthru or {}) // { inherit forceLibgccToBuildCrtStuff; };
   preUnpack = ''
     oldOpts="$(shopt -po nounset)" || true
     set -euo pipefail

pkgs/development/compilers/gcc/common/libgcc-buildstuff.nix

@@ -0,0 +1,37 @@
+{ lib
+, stdenv
+}:
+
+# Trick to build a gcc that is capable of emitting shared libraries *without* having the
+# targetPlatform libc available beforehand.  Taken from:
+#   https://web.archive.org/web/20170222224855/http://frank.harvard.edu/~coldwell/toolchain/
+#   https://web.archive.org/web/20170224235700/http://frank.harvard.edu/~coldwell/toolchain/t-linux.diff
+let
+  # crt{i,n}.o are the first and last (respectively) object file
+  # linked when producing an executable.  Traditionally these
+  # files are delivered as part of the C library, but on GNU
+  # systems they are in fact built by GCC.  Since libgcc needs to
+  # build before glibc, we can't wait for them to be copied by
+  # glibc.  At this early pre-glibc stage these files sometimes
+  # have different names.
+  crtstuff-ofiles =
+    if stdenv.targetPlatform.isPower
+    then "ecrti.o ecrtn.o ncrti.o ncrtn.o"
+    else "crti.o crtn.o";
+
+  # Normally, `SHLIB_LC` is set to `-lc`, which means that
+  # `libgcc_s.so` cannot be built until `libc.so` is available.
+  # The assignment below clobbers this variable, removing the
+  # `-lc`.
+  #
+  # On PowerPC we add `-mnewlib`, which means "libc has not been
+  # built yet".  This causes libgcc's Makefile to use the
+  # gcc-built `{e,n}crt{n,i}.o` instead of failing to find the
+  # versions which have been repackaged in libc as `crt{n,i}.o`
+  #
+  SHLIB_LC = lib.optionalString stdenv.targetPlatform.isPower "-mnewlib";
+
+in ''
+    echo 'libgcc.a: ${crtstuff-ofiles}' >> libgcc/Makefile.in
+    echo 'SHLIB_LC=${SHLIB_LC}' >> libgcc/Makefile.in
+  ''

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

@@ -44,14 +44,14 @@ lib.optional (lib.versionAtLeast version "11.0")
     !langJit &&
     !stdenv.hostPlatform.isDarwin &&
     enableShared
-    ;
+  ;
 
-    # For some reason libgcc_s.so has major-version "2" on m68k but
-    # "1" everywhere else.  Might be worth changing this to "*".
-    libgcc_s-version-major =
-      if targetPlatform.isM68k
-      then "2"
-      else "1";
+  # For some reason libgcc_s.so has major-version "2" on m68k but
+  # "1" everywhere else.  Might be worth changing this to "*".
+  libgcc_s-version-major =
+    if targetPlatform.isM68k
+    then "2"
+    else "1";
 
 in
 (pkg: pkg.overrideAttrs (previousAttrs: lib.optionalAttrs ((!langC) || langJit || enableLibGccOutput) {

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

@@ -112,39 +112,5 @@ in lib.optionalString (hostPlatform.isSunOS && hostPlatform.is64bit) ''
   export inhibit_libc=true
 ''
 
-# Trick to build a gcc that is capable of emitting shared libraries *without* having the
-# targetPlatform libc available beforehand.  Taken from:
-#   https://web.archive.org/web/20170222224855/http://frank.harvard.edu/~coldwell/toolchain/
-#   https://web.archive.org/web/20170224235700/http://frank.harvard.edu/~coldwell/toolchain/t-linux.diff
 + lib.optionalString (targetPlatform != hostPlatform && withoutTargetLibc && enableShared)
-  (let
-
-    # crt{i,n}.o are the first and last (respectively) object file
-    # linked when producing an executable.  Traditionally these
-    # files are delivered as part of the C library, but on GNU
-    # systems they are in fact built by GCC.  Since libgcc needs to
-    # build before glibc, we can't wait for them to be copied by
-    # glibc.  At this early pre-glibc stage these files sometimes
-    # have different names.
-    crtstuff-ofiles =
-      if targetPlatform.isPower
-      then "ecrti.o ecrtn.o ncrti.o ncrtn.o"
-      else "crti.o crtn.o";
-
-    # Normally, `SHLIB_LC` is set to `-lc`, which means that
-    # `libgcc_s.so` cannot be built until `libc.so` is available.
-    # The assignment below clobbers this variable, removing the
-    # `-lc`.
-    #
-    # On PowerPC we add `-mnewlib`, which means "libc has not been
-    # built yet".  This causes libgcc's Makefile to use the
-    # gcc-built `{e,n}crt{n,i}.o` instead of failing to find the
-    # versions which have been repackaged in libc as `crt{n,i}.o`
-    #
-    SHLIB_LC = lib.optionalString targetPlatform.isPower "-mnewlib";
-
-  in ''
-    echo 'libgcc.a: ${crtstuff-ofiles}' >> libgcc/Makefile.in
-    echo 'SHLIB_LC=${SHLIB_LC}' >> libgcc/Makefile.in
-  '')
-
+  (import ./libgcc-buildstuff.nix { inherit lib stdenv; })