git: adding an option not to build the manual

asciidoc+xsltproc take hours to run

pkgs/applications/version-management/git-and-tools/git/default.nix

@@ -3,6 +3,7 @@
 , libxslt, tcl, tk, makeWrapper
 , svnSupport, subversionClient, perlLibs, smtpPerlLibs
 , guiSupport
+, withManual ? true
 , pythonSupport ? true
 , sendEmailSupport
 }:
@@ -26,8 +27,7 @@ stdenv.mkDerivation {
   patches = [ ./docbook2texi.patch ];
 
   buildInputs = [curl openssl zlib expat gettext cpio makeWrapper]
-    ++ # documentation tools
-       [ asciidoc texinfo xmlto docbook2x
+    ++ stdenv.lib.optionals withManual [ asciidoc texinfo xmlto docbook2x
          docbook_xsl docbook_xml_dtd_45 libxslt ]
     ++ stdenv.lib.optionals guiSupport [tcl tk];
 
@@ -91,7 +91,7 @@ stdenv.mkDerivation {
         notSupported $out/libexec/git-core/git-send-email "reinstall with config git = { sendEmailSupport = true } set"
        '')
 
-   + ''# Install man pages and Info manual
+   + stdenv.lib.optionalString withManual ''# Install man pages and Info manual
        make -j $NIX_BUILD_CORES -l $NIX_BUILD_CORES PERL_PATH="${perl}/bin/perl" cmd-list.made install install-info \
          -C Documentation ''