UnitTestFrameworkPkg: Set host application stack size to 256KB

UnitTestFrameworkPkg: Set host application stack size to 256KB

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2803

The UEFI Specification defines the minimum stack size before
ExitBootServices() to be 128KB.  When running a host based unit
test, there may be additional stack overhead from the host
application environment and cmocka.

Update the build flags to set the size of the stack to 256KB
which is double the UEFI Specification requirement.

Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Bret Barkelew <Bret.Barkelew@microsoft.com>