OvmfPkg/build.sh: Use GCC49 toolchains with GCC 6.[0-2]
OvmfPkg/build.sh: Use GCC49 toolchains with GCC 6.[0-2]

The goal of the patch is to avoid using -flto with GCC 6.0 to 6.2.

This is to workaround a GCC bug:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70955

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Anthony PERARD <bd4ca9e282b840f7a66451c0c1b8fcfed96ac883@citrix.com>
Reviewed-by: Laszlo Ersek <7437296077edea1cb64451c122c4dac071f0cfbc@redhat.com>
Regression-tested-by: Laszlo Ersek <7437296077edea1cb64451c122c4dac071f0cfbc@redhat.com>

MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2