[PATCH v2 5/6] Libsanitizer merge from upstream r250806 (was r249633).

[Maxim Ostapenko <m.ostapenko@partner.samsung.com>]

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This patch adjusts the fix for 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61771 to extract the last 
PC from the stack frame if no valid FP is available for ARM. The patch 
was preapproved here: 
(https://gcc.gnu.org/ml/gcc-patches/2015-10/msg01217.html).

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2015-10-20  Maxim Ostapenko  <m.ostapenko@partner.samsung.com>

	* sanitizer_common/sanitizer_stacktrace.cc (GetCanonicFrame): Assume we
	compiled code with GCC when extracting the caller PC for ARM if no
	valid frame pointer is available.

Index: libsanitizer/sanitizer_common/sanitizer_stacktrace.cc
===================================================================
--- libsanitizer/sanitizer_common/sanitizer_stacktrace.cc	(revision 250059)
+++ libsanitizer/sanitizer_common/sanitizer_stacktrace.cc	(working copy)
@@ -62,8 +62,8 @@
   // Nope, this does not look right either. This means the frame after next does
   // not have a valid frame pointer, but we can still extract the caller PC.
   // Unfortunately, there is no way to decide between GCC and LLVM frame
-  // layouts. Assume LLVM.
-  return bp_prev;
+  // layouts. Assume GCC.
+  return bp_prev - 1;
 #else
   return (uhwptr*)bp;
 #endif