haskell: extend generic builder to recognize mis-configured Cabal 2.x…

… builds

Cabal 1.x says:

 | Warning: This package indirectly depends on multiple versions of the same
 | package. This is highly likely to cause a compile failure.

But in version 2.x, that warning is split into two lines differently:

 | Warning:
 |     This package indirectly depends on multiple versions of the same package. This is very likely to cause a compile failure.

This commit modifies the call to "egrep" to recognize both versions by virtue
of the "-z" flag, which essentially interprets the whole configure-time output
as one long line.

pkgs/development/haskell-modules/generic-builder.nix

@@ -276,7 +276,7 @@ stdenv.mkDerivation ({
 
     echo configureFlags: $configureFlags
     ${setupCommand} configure $configureFlags 2>&1 | ${coreutils}/bin/tee "$NIX_BUILD_TOP/cabal-configure.log"
-    if ${gnugrep}/bin/egrep -q '^Warning:.*depends on multiple versions' "$NIX_BUILD_TOP/cabal-configure.log"; then
+    if ${gnugrep}/bin/egrep -q -z 'Warning:.*depends on multiple versions' "$NIX_BUILD_TOP/cabal-configure.log"; then
       echo >&2 "*** abort because of serious configure-time warning from Cabal"
       exit 1
     fi