Revert "detect_cxx_stdlibs: ignore executables."

This reverts commit 1cd636d368c66d1346adc1c38633c8f204c759f4.

Library/Homebrew/keg_fix_install_names.rb

@@ -70,7 +70,6 @@ class Keg
     results = Set.new
 
     mach_o_files.each do |file|
-      next if file.mach_o_executable?
       dylibs = file.dynamically_linked_libraries
       results << :libcxx unless dylibs.grep(/libc\+\+.+\.dylib/).empty?
       results << :libstdcxx unless dylibs.grep(/libstdc\+\+.+\.dylib/).empty?