* gas-bison.y: Add support for .value alias for .2byte (GAS-x86/amd64).

* gas-bison.y: Add support for .value alias for .2byte (GAS-x86/amd64).
This is generated by GCC in debug sections.
* gas-token.re: Likewise.

* gas-bison.y: Add support for 4th parameter on .section directive, for use
with M (SHF_MERGE) ELF section flag.
* elf-objfmt.c: Add support for M, S (SHF_STRINGS), G (SHF_GROUP), and T
(SHF_TLS) section flags.
* elf.h: Declare additional SHF_* flags.

With these changes, debug information generated by GCC in GAS format is
passed through successfully.  Should just need line number generation to
have full debugging for ELF-DWARF2 coming from GCC.

Only remaining thing to handle that I see at the moment for full GCC output
support is multiple instructions on one line (separated by semicolons).

svn path=/trunk/yasm/; revision=1289