[libunwind] Don't use dl_iterate_phdr if __ANDROID_API__ < 21

Summary:
On ARM, dl_iterate_phdr is only implemented in the Android NDK version 21 or later:
https://android.googlesource.com/platform/prebuilts/ndk/+/dev/platform/sysroot/usr/include/link.h#55

Reviewers: thakis, danalbert

Reviewed By: danalbert

Subscribers: dtzWill, aemerson, srhines, kristof.beyls

Differential Revision: https://reviews.llvm.org/D39468

llvm-svn: 317125
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 9288938561af7cb9ad18df553728ee01d31d2e37
diff --git a/src/AddressSpace.hpp b/src/AddressSpace.hpp
index f7cb767..3242840 100644
--- a/src/AddressSpace.hpp
+++ b/src/AddressSpace.hpp
@@ -393,6 +393,14 @@
     }
   }
   return false;
+#elif defined(_LIBUNWIND_ARM_EHABI) && defined(__BIONIC__) &&                  \
+    (__ANDROID_API__ < 21)
+  int length = 0;
+  info.arm_section =
+      (uintptr_t)dl_unwind_find_exidx((_Unwind_Ptr)targetAddr, &length);
+  info.arm_section_length = (uintptr_t)length;
+  if (info.arm_section && info.arm_section_length)
+    return true;
 #elif defined(_LIBUNWIND_ARM_EHABI) || defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
   struct dl_iterate_cb_data {
     LocalAddressSpace *addressSpace;