mkmf: grep all occurrences in cpp output

Apple clang aborts if cpp output is closed in middle, and leaves the
preprocessed source and reproduction shell script.

1 files changed, 2 insertions, 4 deletions

diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index 5f7a7d352a..39ba4030cc 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -931,11 +931,9 @@ SRC
     xpopen(cpp_command('', opt)) do |f|
       if Regexp === pat
         puts("    ruby -ne 'print if #{pat.inspect}'")
-        f.grep(pat) {|l|
+        !f.grep(pat) {|l|
           puts "#{f.lineno}: #{l}"
-          return true
-        }
-        false
+        }.empty?
       else
         puts("    egrep '#{pat}'")
         system("egrep", pat, in: f)