OvmfPkg/build.sh: Support GCC48 toolchain

If GCC 4.8 or 4.9 is detected, then use the GCC48 toolchain.

Previously we would use the GCC47 toolchain, but GCC48
was recently added to the main edk2 BaseTools/Conf.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15141 6f19259b-4bc3-4df7-8a09-765794883524
OvmfPkg: unify PcdMaxVariableSize at 0x2000 bytes

The Linux persistent store (pstore) feature serves, among other things,
for saving the trailing portion of the dmesg in case of a kernel oops. One
backend for the pstore facility is "efivars", ie. non-volatile UEFI
variables.

Linux splits the tail of the dmesg that is to be dumped in 1KB chunks, and
tries to save each chunk as a specially (and differently) named
non-volatile variable. The 1KB chunk size accounts for the variable data
only; Linux expects this size to be available per variable *without*
accounting for the variable name or any firmware-internal overhead.

For non-authenticated (ie. non-secure-boot) variables, OvmfPkg currently
sets the per-variable limit to 0x400 (1KB) through PcdMaxVariableSize.
However this PCD determines the size *before* subtracting the internal
overhead (which is sizeof(VARIABLE_HEADER) == 0x20 bytes for
non-authenticated variables, see
"MdeModulePkg/Include/Guid/VariableFormat.h"), and also before subtracting
the given variable's UCS-2 encoded name (including the trailing 0x0000).

Linux maximizes these special variable names in DUMP_NAME_LEN==52 code
points (including the trailing NUL). Hence we must provide at least

  0x020 == sizeof(VARIABLE_HEADER), for the internal overhead
  0x068 == 2 * 52, for the UCS-2 encoded name, including trailing 0x0000
  0x400 for the variable body
  -----
  0x488 == 1160

bytes in PcdMaxVariableSize, so that Linux's efivars-backed pstore can
work even on non-secure-boot builds of OVMF.

However, as PcdMaxVariableSize=0x2000 has proven reasonable when secure
boot is enabled, it should also be okay when secure boot is disabled; so
for simplicity's sake set PcdMaxVariableSize to 0x2000 unconditionally.

Tested-by: Seiji Aguchi <seiji.aguchi@hds.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15142 6f19259b-4bc3-4df7-8a09-765794883524