BaseTools/tools_def: drop -mgeneral-regs-only for AArch64 CLANGDWARF

Commit 0df6c8c ("BaseTools/tools_def AARCH64:
avoid SIMD registers in XIP code")
adds -mgeneral-regs-only to GCC_AARCH64_CC_XIPFLAGS,
in order to avoid a bug present in certain versions of GCC.
This was never a problem for clang.
That's given the history of what the problem is.
Then we can describe how we fix it:
Change *_CLANGDWARF_AARCH64_CC_XIPFLAGS to set the required -mstrict-align
option instead of importing the whole GCC variable.

Signed-off-by: Yeping Song <quic_yepings@quicinc.com>
Cc: Rebecca Cran <rebecca@bsdio.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Yuwei Chen <yuwei.chen@intel.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Leif Lindholm <quic_llindhol@quicinc.com>
Cc: Sami Mujawar <sami.mujawar@arm.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Leif Lindholm <quic_llindhol@quicinc.com>

Author: Yepingsong

BaseTools/Conf/tools_def.template

@@ -2015,7 +2015,7 @@ DEFINE CLANGDWARF_AARCH64_DLINK_FLAGS  = DEF(CLANGDWARF_AARCH64_TARGET) DEF(GCC_
 *_CLANGDWARF_AARCH64_RC_FLAGS       = DEF(GCC_AARCH64_RC_FLAGS) DEF(GCC_AARCH64_RC_BTI_FLAGS)
 *_CLANGDWARF_AARCH64_VFRPP_FLAGS    = DEF(GCC_VFRPP_FLAGS) DEF(CLANGDWARF_AARCH64_TARGET) $(PLATFORM_FLAGS)
 *_CLANGDWARF_AARCH64_ASLPP_FLAGS    = DEF(GCC_ASLPP_FLAGS) DEF(CLANGDWARF_AARCH64_TARGET)
-*_CLANGDWARF_AARCH64_CC_XIPFLAGS    = DEF(GCC_AARCH64_CC_XIPFLAGS)
+*_CLANGDWARF_AARCH64_CC_XIPFLAGS    = -mstrict-align
 
   DEBUG_CLANGDWARF_AARCH64_CC_FLAGS    = DEF(CLANGDWARF_AARCH64_CC_FLAGS) $(PLATFORM_FLAGS) -flto -O1
   DEBUG_CLANGDWARF_AARCH64_DLINK_FLAGS = DEF(CLANGDWARF_AARCH64_DLINK_FLAGS) -flto -Wl,-O1 -fuse-ld=lld -L$(WORKSPACE)/ArmPkg/Library/GccLto -llto-aarch64 -Wl,-plugin-opt=-pass-through=-llto-aarch64 -Wl,--no-pie,--no-relax