Fix inputproto and probably other packages

"grep Requires" failed on *.pc files that had no Requires fields, due
to pipefail. But this error was previously masked by #7524.

pkgs/servers/x11/xorg/builder.sh

@@ -9,8 +9,10 @@ postInstall() {
     if test -n "$origPostInstall"; then eval "$origPostInstall"; fi
 
     local r p requires
+    set +o pipefail
     requires=$(grep "Requires:" $out/lib/pkgconfig/*.pc | \
         sed "s/Requires://" | sed "s/,/ /g")
+    set -o pipefail
 
     echo "propagating requisites $requires"