Update prebuilt flex-2.5.4a to i386

Update prebuilt flex-2.5.4a to i386

The version of flex 2.5.4 included in prebuilt was compiled for the
ppc architecture.

OS X 10.6 (Snow Leopard) does not install Rosetta by default to allow the
execution of ppc binaries, which causes build issues with webkit on that
platform. This commit is a fresh compile of flex 2.5.4 as an i386 binary
which should work for all darwin-x86 platforms.

The build error encountered:
Target Generated: libwebcore <= external/webkit/WebCore/css/tokenizer.flex
You need the Rosetta software to run flex-2.5.4a. The Rosetta installer is
in Optional Installs on your Mac OS X installation disc.

The output of "lipo -info flex-2.5.4a" before commit:
Non-fat file: flex-2.5.4a is architecture: ppc

Output of "lipo -info flex-2.5.4a" with this change:
Non-fat file: flex-2.5.4a is architecture: i386

Binary was compiled with gcc-4.0 with the -arch i386 flag.