Instead of adding SQLITE_API macros sqlite3.h while creating sqlite3.c, add them...

Instead of adding SQLITE_API macros sqlite3.h while creating sqlite3.c, add them as part of generating the sqlite3.h target, while copying from sqlite.h.in to sqlite3.h. This fixes a build problem that was causing multiple SQLITE_API macros to be added to a single line of sqlite3.h, and the problem cited by #4016. (CVS 6971)

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