ArmPkg: rewrite vector table population macros

Unfortunately, Clang does not support the use of symbol references in .org
directives, and bails with the following error message when it encounters
them:

  <...>:error: expected assembly-time absolute expression
  .org DebugAgentVectorTable + 0x000

So replace the .org arguments with absolute values, and move the whole
vector table into a subsection with the appropriate alignment, and
starting at .org 0x0. This gives the same protection with respect to
entries that exceed 128 bytes, in a way that Clang supports as well.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19303 6f19259b-4bc3-4df7-8a09-765794883524

ArmPkg/Include/Chipset/AArch64.h

@@ -119,15 +119,18 @@
 #define ARM_VECTOR_LOW_A32_SERR 0x780
 
 #define VECTOR_BASE(tbl)          \
+  .section .text.##tbl##,"ax";    \
   .align 11;                      \
+  .org 0x0;                       \
   GCC_ASM_EXPORT(tbl);            \
   ASM_PFX(tbl):                   \
 
 #define VECTOR_ENTRY(tbl, off)    \
-  .org ASM_PFX(tbl) + off
+  .org off
 
 #define VECTOR_END(tbl)           \
-  .org ASM_PFX(tbl) + 0x800
+  .org 0x800;                     \
+  .previous
 
 VOID
 EFIAPI