Add WOLFSSL_BARMETAL macro #1

Job	Run time
Bare-metal build (autotools) (--enable-baremetal)	1m 36s
Bare-metal build (CMake) (true)	36s
Bare-metal build (autotools) (--enable-baremetal --enable-cryptonly)	40s
Bare-metal build (CMake) (false)	48s
	3m 40s

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