Remove no longer needed change in mkmf.rb

* We do normal compilation with the toolchain, so tweaking the object
  extension should no longer be needed.

Author: eregon

lib/mri/mkmf.rb

@@ -576,14 +576,8 @@ def cc_command(opt="")
     conf = RbConfig::CONFIG.merge('hdrdir' => $hdrdir.quote, 'srcdir' => $srcdir.quote,
                                   'arch_hdrdir' => $arch_hdrdir.quote,
                                   'top_srcdir' => $top_srcdir.quote)
-    if defined?(::TruffleRuby)
-      # Specify output file (-o) explictly. Clang 3.8 produces conftest.o and 3.9 conftest.bc.
-      RbConfig::expand("$(CC) #$INCFLAGS #$CPPFLAGS #$CFLAGS #$ARCH_FLAG #{opt} -o #{CONFTEST}.#{$OBJEXT} -c #{CONFTEST_C}",
-                       conf)
-    else
-      RbConfig::expand("$(CC) #$INCFLAGS #$CPPFLAGS #$CFLAGS #$ARCH_FLAG #{opt} -c #{CONFTEST_C}",
-                       conf)
-    end
+    RbConfig::expand("$(CC) #$INCFLAGS #$CPPFLAGS #$CFLAGS #$ARCH_FLAG #{opt} -c #{CONFTEST_C}",
+                     conf)
   end
 
   def cpp_command(outfile, opt="")