optimize: use more appressive JIT compiler parameters as the default to help large OpenResty Lua apps.

We now use the following jit.opt defaults:

maxtrace=8000
maxrecord=16000
minstitch=3
maxmcode=40960  -- in KB

Reported by Yichun Zhang.

Contributed by Peter Cawley.

Thanks to Joshua Haberman.

Thanks to Peter Cawley.

Contributed by Djordje Kovacevic and Stefan Pejic from RT-RK.com.
Sponsored by Cisco Systems, Inc.

Contributed by Peter Cawley.

Signed-off-by: Yichun Zhang (agentzh) <agentzh@gmail.com>

Contributed by Djordje Kovacevic and Stefan Pejic from RT-RK.com.
Sponsored by Cisco Systems, Inc.

bugfix: fixed a clang warning in lj_str.c regarding unused str_fastcmp() when macro LUAJIT_USE_VALGRIND is defined.

bugfix: FFI C parsers could not parse some C constructs like `__attribute((aligned(N)))` and `#pragma`.

Decoupled hash functions used in comparison (hardcoded) and string table.

This bug had first appeared in v2.1-20170405 (or OpenResty 1.11.2.3).

Signed-off-by: Yichun Zhang (agentzh) <agentzh@gmail.com>

Suggested by 罗泽轩.

Contributed by Djordje Kovacevic and Stefan Pejic from RT-RK.com.
Sponsored by Cisco Systems, Inc.

Contributed by Djordje Kovacevic and Stefan Pejic.

Contributed by Djordje Kovacevic and Stefan Pejic.

Thanks to Yichun Zhang.

Thanks to Yichun Zhang.