GDBJIT: Make GDBJIT interface compile for OSX again.

GDBJIT: Make GDBJIT interface compile for OSX again.

[haitao.feng, 2013-03-26 06:48:27]

I built gdb 7.4 from http://ftp.gnu.org/gnu/gdb/ on Mac OSX 10.7.5.

With this CL, gdbjit compiles for both gyp and scons while currently it only
works for d8_g built from scons, not d8 from gyp. I know I should build with
GYP, but currently I did not figure out which option or change caused that gdb
7.4 does not work for d8 with gdbjit built from gyp on Mac.

[Vyacheslav Egorov (Google), 2013-03-26 11:28:36]

gdb-jit parts LGTM, but I don't know if we still accept any changes to
SConstruct given that it is deprecated.

Jakob, do we accept SConstruct changes?

[Jakob Kummerow, 2013-03-26 12:02:37]

All Scons-related files in our repository are awaiting removal, there's no point
in making any changes to them.

[haitao.feng, 2013-03-27 07:59:31]

I figured out the difference between gyp and scons. Scons links all the obj
files together for d8_g, gyp uses libtool to build libv8_base.a and
libv8_snapshot.a and links the other obj files with those two libraries. I used
a single command to link all the gyp generated ob files for d8 and gdbjit works
for it. I did not investigate further the interaction between gdbjit and
libtool.

[haitao.feng, 2013-04-10 09:11:50]

Dropped the code modification to src/SConscipt as scons is going to die.

Though gdb-jit compiles for Mac with gyp, it might not work properly like on
Linux. We need to debug into gdb to understand the reason.