Evaluate whether to adopt any compiler flags set by debian

[flavorjones]

Debian currently sets these flags (as of sid/unstable 3.46.1-1, see http://deb.debian.org/debian/pool/main/s/sqlite3/sqlite3_3.46.1-1.debian.tar.xz)

export CFLAGS += -O2 -fno-strict-aliasing \
    -DSQLITE_SECURE_DELETE -DSQLITE_ENABLE_COLUMN_METADATA \
    -DSQLITE_ENABLE_FTS3 -DSQLITE_ENABLE_FTS3_PARENTHESIS \
    -DSQLITE_ENABLE_RTREE=1 -DSQLITE_SOUNDEX=1 \
    -DSQLITE_ENABLE_UNLOCK_NOTIFY \
    -DSQLITE_ENABLE_DBSTAT_VTAB \
    -DSQLITE_ALLOW_ROWID_IN_VIEW \
    -DSQLITE_ENABLE_UPDATE_DELETE_LIMIT=1 \
    -DSQLITE_ENABLE_LOAD_EXTENSION \
    -DSQLITE_ENABLE_JSON1 \
    -DSQLITE_LIKE_DOESNT_MATCH_BLOBS \
    -DSQLITE_THREADSAFE=1 \
    -DSQLITE_ENABLE_FTS3_TOKENIZER=1 \
    -DSQLITE_USE_URI=1 \
    -DSQLITE_MAX_SCHEMA_RETRY=25 \
    -DSQLITE_ENABLE_PREUPDATE_HOOK \
    -DSQLITE_ENABLE_SESSION \
    -DSQLITE_ENABLE_STMTVTAB \
    -DSQLITE_STRICT_SUBTYPE=1 \
    -DSQLITE_MAX_VARIABLE_NUMBER=250000

Any of these make sense for this gem to set when it compiles?

[flavorjones]

Because #605 is showing that the new autoconf amalgamations are NOT working properly, I'm working on using the plain amalgamation and will pull these preprocessor defs into that PR.

[flavorjones]

Related, see #636 which is a branch using the plain amalgamation and these CPP flags.