re PR c/7054 (#pragma pack handled incorrectly)

re PR c/7054 (#pragma pack handled incorrectly)

        PR c/7054
        * defaults.h (TARGET_DEFAULT_PACK_STRUCT): Provide default.
        * tree.h (initial_max_fld_align): Declare
        * stor-layout.c (initial_max_fld_align): Define and initialize.
        (maximum_field_alignment): Initialize to the same value.
        * common.opt: Add -fpack-struct= variant of switch.
        * opts.c: Handle -fpack-struct= variant of switch.
        * c-pragma.c: Change #pragma pack() handling so that it becomes
        compatible to other compilers: accept individual 'push' argument,
        make final pop restore (command line) default, correct interaction
        of push/pop and sole specification of a new alignment (so that the
        sequence #pragma pack(push) - #pragma pack(<n>) becomes identical
        to #pragma pack(push, <n>).
        * doc/extend.texi: New node "Structure-Packing Pragmas" under
        "Pragmas", describing #pragma pack.
        * doc/invoke.texi: Document -fpack-struct=<n> variant of switch.
        * doc/tm.texi: Adjust description for HANDLE_PRAGMA_PACK_PUSH_POP.
        Document new TARGET_DEFAULT_PACK_STRUCT.
testsuite:
        * gcc.dg/pack-test-2.c: Adjust to permit and check #pragma pack(push).
        * gcc.dg/c99-flex-array-4.c: Add -fpack-struct=8 to provide a
        deterministic starting point for the alignment of structure fields.
        * gcc.dg/Wpadded.c: Dito.
        * g++.dg/abi/vbase10.C: Dito.

From-SVN: r87037