mutt: avoid build-only references in 'mutt -v'

The change removes `gcc` from runtime closure. This shrinks closure in
half.

Before the change:

    nix path-info -Sh $(nix-build -A mutt) |& unnix
    $ /<<NIX>>/mutt-2.2.10     440.0M

After the change: 218M

    $ nix path-info -Sh $(nix-build -A mutt) |& unnix
    /<<NIX>>/mutt-2.2.10     218.7M

pkgs/applications/networking/mailreaders/mutt/default.nix

@@ -31,7 +31,10 @@ stdenv.mkDerivation rec {
     sha256 = "sha256-TXc/IkIveQlve5S1e+5FZUrZolFl27NkY8WClbTNPYg=";
   };
 
-  patches = lib.optional smimeSupport (fetchpatch {
+  patches = [
+    # Avoid build-only references embedding into 'mutt -v' output.
+    ./no-build-only-refs.patch
+  ] ++ lib.optional smimeSupport (fetchpatch {
     url = "https://salsa.debian.org/mutt-team/mutt/raw/debian/1.10.1-2/debian/patches/misc/smime.rc.patch";
     sha256 = "0b4i00chvx6zj9pcb06x2jysmrcb2znn831lcy32cgfds6gr3nsi";
   });

pkgs/applications/networking/mailreaders/mutt/no-build-only-refs.patch

@@ -0,0 +1,24 @@
+Avoid build-only store references embedding into 'mutt -v'.
+--- a/txt2c.sh
++++ b/txt2c.sh
+@@ -21,8 +21,18 @@ txt2c_fallback () {
+ 	echo ";"
+ }
+ 
++nix_store_mangle() {
++	# consume stdin
++
++	# Avoid build-only references to nix store. These are usually
++	# 'gcc -v' output embedded into 'mutt -v'. But also might be
++	# ./configure-passed arguments.
++	sed \
++	    -e 's@'$NIX_STORE'/[a-z0-9]\{32\}-@/<<NIX>>/@g'
++}
++
+ if ./txt2c test </dev/null >/dev/null 2>&1; then
+-    ./txt2c "$1"
++    nix_store_mangle | ./txt2c "$1"
+ else
+-    txt2c_fallback "$1"
++    nix_store_mangle | txt2c_fallback "$1"
+ fi