Decouple outdated SQLite3 Btree dependency

[ComFreek]

Right now, the module src/runtime/c/sg includes a custom version (namely sqlite3Btree.{c,h}) of an outdated snapshot of SQLite's source.
These files mention functions such as sqlite3StrICmp which are nowhere defined and are thus leading to undefined reference errors; at least when building for Windows which does not allow unknown references in shared libraries afaik. See also https://groups.google.com/forum/#!topic/gf-dev/BkYwEl0SE00 where the exact issued build instructions can be found.

I tried replacing sqlite3Btree.{c,h} by the most recent SQLite3 amalgamation files, however, the internal API of sqlite3Btree changed.
For example, the old sqlite3BtreeInsert's function signature contained in this repository looks like

GF/src/runtime/c/sg/sqlite3Btree.h

Lines 601 to 603 in 6cf80c0

	int sqlite3BtreeInsert(BtCursor*, const void *pKey, i64 nKey,
	const void *pData, int nData,
	int nZero, int bias, int seekResult);

but the current one (as found in the amalgamation sqlite3.c) looks like

SQLITE_PRIVATE int sqlite3BtreeInsert(BtCursor*, const BtreePayload *pPayload,
                       int flags, int seekResult);

As SQLITE_PRIVATE also indicates, the Btree API was never meant to be stable and publicly accessible.

[ComFreek]

Follow-up: I got a cross-compilation from Ubuntu to Windows working by manually defining all missing functions (i.e. copy-pasting from the SQLite source until all references were saturated):

• https://github.com/ComFreek/reproducible-gf-runtime/blob/7f615048e86d12488a4bcdb12c8b123fd017c638/sqlite3-fix.c
• which is included by the build script in src/runtime/c/sg/sg.c: https://github.com/ComFreek/reproducible-gf-runtime/blob/7f615048e86d12488a4bcdb12c8b123fd017c638/build-win.sh#L34

Still, I hope this issue gets fixed since my hacky approach probably introduced a handful of bugs and logical inconsistencies in addition to those already present in the outdated SQLite source contained in this repo.