Set CFLAGS differently for linux and osx.

Add check for linux and move initial CFLAG settings inside linux check. Add
CFLAGS specific to osx and clang to the existing osx/darwin check. Ignore clang warning about default on covered enum switch, look at pull #217 and pull #177 for more info about why that warning is ignored on clang. Ignore unknown clang options so that I don't have to change CFLAG settings elsewhere in the file, clang should just ignore options it dosen't know about.

test/Makefile

 CC = gcc
 ifeq ($(shell uname -s), Darwin)
 CC = clang
+CFLAGS += -std=c99 -pedantic -Wall -Weverything -Werror
+CFLAGS += -Wno-unknown-warning-option -Wno-switch-enum
 endif
-#DEBUG = -O0 -g
+ifeq ($(shell uname -s), Linux)
 CFLAGS += -std=c99 -pedantic -Wall -Wextra -Werror
+endif
+#DEBUG = -O0 -g
 CFLAGS += $(DEBUG)
 DEFINES =  -D UNITY_OUTPUT_CHAR=putcharSpy
 DEFINES += -D UNITY_SUPPORT_64 -D UNITY_INCLUDE_DOUBLE -D UNITY_NO_WEAK