Fix linter warnings.

Author: aardvark179

lib/truffle/rbconfig-for-mkmf.rb

@@ -143,18 +143,18 @@
     "#{compiler} -I$(<D) #{flags} - -o $@ && #{opt_command}"
   end
 
-  c_flags = "$(INCFLAGS) $(CPPFLAGS) $(CFLAGS) $(COUTFLAG) -xc"
-  cxx_flags = "$(INCFLAGS) $(CPPFLAGS) $(CXXFLAGS) $(COUTFLAG) -xc++"
+  c_flags = '$(INCFLAGS) $(CPPFLAGS) $(CFLAGS) $(COUTFLAG) -xc'
+  cxx_flags = '$(INCFLAGS) $(CPPFLAGS) $(CXXFLAGS) $(COUTFLAG) -xc++'
   opt_command = "#{opt} #{opt_passes} $@ -o $@"
 
-  mkconfig["TRUFFLE_RAW_COMPILE_C"] = for_file.call("$(CC)", c_flags, opt_command)
+  mkconfig['TRUFFLE_RAW_COMPILE_C'] = for_file.call("$(CC)", c_flags, opt_command)
   mkconfig['COMPILE_C']   = with_conditional_preprocessing.call(
-    for_pipe.call("$(CC)", c_flags, opt_command),
-    for_file.call("$(CC)", c_flags, opt_command))
+    for_pipe.call('$(CC)', c_flags, opt_command),
+    for_file.call('$(CC)', c_flags, opt_command))
 
   mkconfig['COMPILE_CXX']   = with_conditional_preprocessing.call(
-    for_pipe.call("$(CXX)", cxx_flags, opt_command),
-    for_file.call("$(CXX)", cxx_flags, opt_command))
+    for_pipe.call('$(CXX)', cxx_flags, opt_command),
+    for_file.call('$(CXX)', cxx_flags, opt_command))
 end
 
 # From mkmf.rb: "$(CC) #{OUTFLAG}#{CONFTEST}#{$EXEEXT} $(INCFLAGS) $(CPPFLAGS) $(CFLAGS) $(src) $(LIBPATH) $(LDFLAGS) $(ARCH_FLAG) $(LOCAL_LIBS) $(LIBS)"