[hwasan][aarch64] Fix missing DT_AARCH64_BTI_PLT flag (#95796)

When building hwasan on aarch64, the DT_AARCH64_BTI_PLT flag is missing
from libclang_rt.hwasan.so because some object files without
DT_AARCH64_BTI_PLT are linked in the final DSO.
These files are specific to riscv64 and x86_64, ending up with no
aarch64 code in them.

Avoid building and linking architecture-specific files unless the
architecture is listed in HWASAN_SUPPORTED_ARCH.

compiler-rt/lib/hwasan/CMakeLists.txt

@@ -15,16 +15,28 @@ set(HWASAN_RTL_SOURCES
   hwasan_memintrinsics.cpp
   hwasan_poisoning.cpp
   hwasan_report.cpp
-  hwasan_setjmp_aarch64.S
-  hwasan_setjmp_riscv64.S
-  hwasan_setjmp_x86_64.S
-  hwasan_tag_mismatch_aarch64.S
-  hwasan_tag_mismatch_riscv64.S
   hwasan_thread.cpp
   hwasan_thread_list.cpp
   hwasan_type_test.cpp
   )
 
+foreach(arch ${HWASAN_SUPPORTED_ARCH})
+  if(${arch} MATCHES "aarch64")
+    list(APPEND HWASAN_RTL_SOURCES
+      hwasan_setjmp_aarch64.S
+      hwasan_tag_mismatch_aarch64.S)
+  endif()
+  if(${arch} MATCHES "riscv64")
+    list(APPEND HWASAN_RTL_SOURCES
+      hwasan_setjmp_riscv64.S
+      hwasan_tag_mismatch_riscv64.S)
+  endif()
+  if(${arch} MATCHES "x86_64")
+    list(APPEND HWASAN_RTL_SOURCES
+      hwasan_setjmp_x86_64.S)
+  endif()
+endforeach()
+
 set(HWASAN_RTL_CXX_SOURCES
   hwasan_new_delete.cpp
   )