--env: show HOMEBREW_CC in superenv

Closes Homebrew/homebrew#18247.

Library/Homebrew/cmd/--env.rb

@@ -19,7 +19,10 @@ module Homebrew extend self
   end
 
   def build_env_keys env
-    %w[ CC CXX LD CFLAGS CXXFLAGS CPPFLAGS LDFLAGS SDKROOT MAKEFLAGS
+    %w[
+      CC CXX LD
+      HOMEBREW_CC
+      CFLAGS CXXFLAGS CPPFLAGS LDFLAGS SDKROOT MAKEFLAGS
       CMAKE_PREFIX_PATH CMAKE_INCLUDE_PATH CMAKE_LIBRARY_PATH CMAKE_FRAMEWORK_PATH
       MACOSX_DEPLOYMENT_TARGET PKG_CONFIG_PATH PKG_CONFIG_LIBDIR
       HOMEBREW_DEBUG HOMEBREW_MAKE_JOBS HOMEBREW_VERBOSE HOMEBREW_USE_CLANG
@@ -31,6 +34,10 @@ module Homebrew extend self
 
   def dump_build_env env
     build_env_keys(env).each do |key|
+      case key when 'CC', 'CXX'
+        next
+      end if superenv?
+
       value = env[key]
       print "#{key}: #{value}"
       case key when 'CC', 'CXX', 'LD'