Fix the following warnings reported by the compiler when
ZDICTLIB_STATIC_API is not defined to ZDICTLIB_API:
lib/dictBuilder/cover.c:1122:21: warning: redeclaration of 'ZDICT_optimizeTrainFromBuffer_cover' with different visibility (old visibility
preserved)
lib/dictBuilder/cover.c:736:21: warning: redeclaration of 'ZDICT_trainFromBuffer_cover' with different visibility (old visibility
+preserved)
lib/dictBuilder/fastcover.c:549:1: warning: redeclaration of 'ZDICT_trainFromBuffer_fastCover' with different visibility (old visibility
preserved)
lib/dictBuilder/fastcover.c:618:1: warning: redeclaration of 'ZDICT_optimizeTrainFromBuffer_fastCover' with different visibility (old
visibility preserved)
zstd-internal was intended to be a helper target, but it doesn't help
at all, what it does in practice is a useless rebuild of zstd every time
"make zstd" is invoked.
Fixes: 030ac243a0 ("Changed Makefile to generate zstd with .gz support by default")