The Mac compiler treats "#pragma pack()" as gcc's "#pragma pack(pop)",
and so dies if the pragma pack stack is empty.  Adding a "#pragma
pack(1)" immediately beforehand is enough to keep the Mac compiler
happy.

The combination of "#pragma pack(1)", "#pragma pack()" won't actually
achieve anything on a Mac, but it will at least build.  (With gcc, the
"#pragma pack()" overrides any previous pragmas, so is still useful.)

Suggested-by: Joshua Oreman <oremanj@rwcr.net>

Eliminate the potential for mismatches between table names and the
table entry data type by incorporating the data type into the
definition of the table, rather than specifying it explicitly in each
table accessor method.

Intel's C compiler (icc) chokes on the zero-length arrays that we
currently use as part of the mechanism for accessing linker table
entries.  Abstract away the zero-length arrays, to make a port to icc
easier.

Introduce macros such as for_each_table_entry() to simplify the common
case of iterating over all entries in a linker table.

Represent table names as #defined string constants rather than
unquoted literals; this avoids visual confusion between table names
and C variable or type names, and also allows us to force a
compilation error in the event of incorrect table names.

Merge in the changes that allow for building EFI driver images (that
can be loaded using the EFI shell's "load" command) as well as EFI
applications.

elf2efi converts a suitable ELF executable (containing relocation
information, and with appropriate virtual addresses) into an EFI
executable.  It is less tightly coupled with the gPXE build process
and, in particular, does not require the use of a hand-crafted PE
image header in efiprefix.S.

elf2efi correctly handles .bss sections, which significantly reduces
the size of the gPXE EFI executable.

EFI passes in copies of SMBIOS and other system configuration tables
via the EFI system table.  Allow configuration tables to be requested
using a mechanism similar to the current method for requesting EFI
protocols.

EFI_STATUS is defined as an INTN, which maps to UINT32 (i.e. unsigned
int) on i386 and UINT64 (i.e. unsigned long) on x86_64.  This would
require a cast each time the error status is printed.

Add efi_strerror() to avoid this ickiness and simultaneously enable
prettier reporting of EFI status codes.

We have EFI APIs for CPU I/O, PCI I/O, timers, console I/O, user
access and user memory allocation.

EFI executables are created using the vanilla GNU toolchain, with the
EXE header handcrafted in assembly and relocations generated by a
custom efilink utility.

The intention is to include near-verbatim copies of the EFI headers
required by gPXE.  This is achieved using the import.pl script in
src/include/gpxe/efi.

Note that import.pl will modify any #include lines in each imported
header to reflect its new location within the gPXE tree.  It will also
tidy up the file by removing carriage return characters and trailing
whitespace.