[flashrom] [patch] more NetBSD fixes (w/ patch)

[Jonathan A. Kollasch]

Cast input to tolower() to unsigned char to work around how tolower() is
implemented on NetBSD.

Also, use CPPFLAGS (rather than overriding CFLAGS) for the
NetBSD/DragonFly build example.

Signed-off-by: Jonathan A. Kollasch 
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