Wrap some exceptionally long lines in main.mk. Add option to override LDFLAGS on...

Wrap some exceptionally long lines in main.mk. Add option to override LDFLAGS on the sqlite3.dll target. Audit: all targets for which it is hypothetically relevant can now inherit user-supplied LDFLAGS, but only those provided to the configure script, not at make-time, in order to mimic the historical build's restriction in that regard.

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