Fix __gnu_Unwind_Find_exidx again.

The math on the size calculation was wrong as the type of
__exidx_start/__exidx_end was unsigned rather than a char. Make a
struct that represents each item instead and remove the division.

Test: built artifacts and used them in the NDK
Bug: None
Change-Id: Ic2c0c123a369b9319e8645d806d659290eb2f69c

libc/arch-arm/bionic/exidx_static.c

@@ -35,10 +35,15 @@
  * EXIDX section.
  */
 
-extern unsigned __exidx_end;
-extern unsigned __exidx_start;
+struct exidx_entry {
+  uint32_t key;
+  uint32_t value;
+};
+
+extern struct exidx_entry __exidx_end;
+extern struct exidx_entry __exidx_start;
 
 _Unwind_Ptr __gnu_Unwind_Find_exidx(_Unwind_Ptr pc __attribute__((unused)), int* pcount) {
-  *pcount = (&__exidx_end - &__exidx_start) / 8;
+  *pcount = (&__exidx_end - &__exidx_start);
   return (_Unwind_Ptr)&__exidx_start;
 }