MdeModulePkg/Core: Decorate phase-transition functions with NORETURN.

This patch adds the NORETURN attribute to functions that transfer to
other phases, along with an UNREACHABLE() call at the end to avoid
false warnings.
DxeIpl has been excluded as its main function returns a status.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Marvin Haeuser <Marvin.Haeuser@outlook.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

MdeModulePkg/Core/Dxe/DxeMain/DxeMain.c

@@ -235,6 +235,7 @@ GLOBAL_REMOVE_IF_UNREFERENCED EFI_LOAD_FIXED_ADDRESS_CONFIGURATION_TABLE    gLoa
 
 **/
 VOID
+NORETURN
 EFIAPI
 DxeMain (
   IN  VOID *HobStart
@@ -524,6 +525,8 @@ DxeMain (
   //
   ASSERT (FALSE);
   CpuDeadLoop ();
+
+  UNREACHABLE ();
 }