In GAS mode, detect sections that are marked as contain code thanks to "x"

In GAS mode, detect sections that are marked as contain code thanks to "x"
flag, not just sections named ".text".

* section.h (yasm_object_get_general): Add code flag parameter to indicate
if section is intended to contain code.
(yasm_section_is_code): New, to get value of code flag.
* section.c (yasm_section): Add flag to section structure.
(yasm_object_get_general, yasm_section_is_code): Implement flag.

* *-objfmt.c, stabs-dbgfmt.c: Update call to yasm_object_get_general,
setting code flag appropriately (only elf *really* handles this correctly,
coff still needs to handle GAS flags to work fully from GAS mode).

* gas-parser.h (yasm_parser_gas): Remove code_section flag.
* gas-bison.y (gas_switch_section): Don't set.
(gas_parser_align): Use yasm_section_is_code() instead of code_section flag.
* gas-parser.c: Don't initialize code_section flag.

svn path=/trunk/yasm/; revision=1318