ruby: Rename removeReferencesToCC flag to !jitSupport

If JIT support is built in to ruby, there's no choice other then to
leave this cc reference as is. removeReferencesToCC didn't do it's job
completely since some time ago. That's why it was practically redundant
- `lib/ruby/${version}/<platform>/rbconfig.rb` still referenced cc.
Removing this reference from
`lib/ruby/${version}/<platform>/rbconfig.rb` as well might lead to
breakage in some Gems that require this feature.

But, if JIT support is not desired, it should be safe enough to
completely remove all cc references, both in
lib/ruby/${version}/<platform>/rbconfig.rb and in $out/lib/libruby.so .
Hence now `rubyMinimal` has JIT support disabled and it has no
references at all to stdenv.cc.

pkgs/development/interpreters/ruby/default.nix

@@ -44,11 +44,23 @@ let
       , groff, docSupport ? true
       , libyaml, yamlSupport ? true
       , libffi, fiddleSupport ? true
-      # ruby -e "puts RbConfig::CONFIG['configure_args']"
-      # puts a reference to the C compiler in the binary.
-      # This might be required by some gems at runtime,
-      # but we allow to strip it out for smaller closure size.
-      , removeReferencesTo, removeReferenceToCC ? true
+      # By default, ruby has 3 observed references to stdenv.cc:
+      #
+      # - If you run:
+      #     ruby -e "puts RbConfig::CONFIG['configure_args']"
+      # - In:
+      #     $out/${passthru.libPath}/${stdenv.targetPlatform.system}/rbconfig.rb
+      #   Or (usually):
+      #     $(nix-build -A ruby)/lib/ruby/2.6.0/x86_64-linux/rbconfig.rb
+      # - In $out/lib/libruby.so and/or $out/lib/libruby.dylib
+      #
+      # Since some Gems require JIT support, there's probably no
+      # escape from this reference. Hence, it was decided to enable this
+      # feature by default, as it's enabled by default by ruby's ./configure
+      # script. We do disable this feature though for the other cc references
+      # in all of the locations given above for the `rubyMinimal` build defined
+      # in all-packages.nix.
+      , removeReferencesTo, jitSupport ? true
       , autoreconfHook, bison, autoconf
       , buildEnv, bundler, bundix
       , libiconv, libobjc, libunwind, Foundation
@@ -121,6 +133,7 @@ let
 
         configureFlags = ["--enable-shared" "--enable-pthread" "--with-soname=ruby-${version}"]
           ++ op useRailsExpress "--with-baseruby=${baseruby}/bin/ruby"
+          ++ op (!jitSupport) "--disable-jit-support"
           ++ op (!docSupport) "--disable-install-doc"
           ++ ops stdenv.isDarwin [
             # on darwin, we have /usr/include/tk.h -- so the configure script detects
@@ -157,11 +170,14 @@ let
           # Remove unnecessary groff reference from runtime closure, since it's big
           sed -i '/NROFF/d' $out/lib/ruby/*/*/rbconfig.rb
           ${
-            lib.optionalString removeReferenceToCC ''
+            lib.optionalString (!jitSupport) ''
               # Get rid of the CC runtime dependency
               ${removeReferencesTo}/bin/remove-references-to \
                 -t ${stdenv.cc} \
                 $out/lib/libruby*
+              ${removeReferencesTo}/bin/remove-references-to \
+                -t ${stdenv.cc} \
+                $out/${passthru.libPath}/${stdenv.targetPlatform.system}/rbconfig.rb
             ''
           }
           # Bundler tries to create this directory

pkgs/top-level/all-packages.nix

@@ -10548,6 +10548,7 @@ in
   rubyMinimal = ruby.override {
     # gem support is minimal overhead
     rubygemsSupport = true;
+    jitSupport = false;
     useRailsExpress = false;
     zlibSupport = false;
     opensslSupport = false;