tools/headerversions.c: fix build without SQLite

[whitslack]

Commit 5318459 broke the build without SQLite because this code:

new = tal_fmt(NULL, template,
              IF_SQLITE3(sqlite3_libversion_number()));

preprocesses into:

new = tal_fmt(NULL, template,
              );

which has a syntax error. Fix it by moving the comma into the macro argument.

Fixes: 5318459
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