Delete warning flags included by -Wall, -Wextra, or produce false postives

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.

 CC always exists inside make so ?= doesn't assign to it

 The C preprocessor cannot use sizeof in #if etc.

 Add config flag for 64-bit, max covered lines even with 32-bit compilers
 Always print uncovered lines, delete separate make target

 Revert the previous commit. Add tests for extended enum cases.
 Fix crash due to accessing 'trait_names' array out of bounds.
 Adding an extra invalid value to the end of an enum causes '-Wswitch' flag
  to warn unless there is a switch default case - also enabled by '-Wall'.

 Unity is at 92% coverage now
 Run 'make -s' to see coverage information for unity.c
 Run 'make uncovered' to get missing lines output