Add support for Elbrus 2000 (e2k) (#889)

absl/base/attributes.h

@@ -121,7 +121,7 @@
 #if ABSL_HAVE_ATTRIBUTE(disable_tail_calls)
 #define ABSL_HAVE_ATTRIBUTE_NO_TAIL_CALL 1
 #define ABSL_ATTRIBUTE_NO_TAIL_CALL __attribute__((disable_tail_calls))
-#elif defined(__GNUC__) && !defined(__clang__)
+#elif defined(__GNUC__) && !defined(__clang__) && !defined(__e2k__)
 #define ABSL_HAVE_ATTRIBUTE_NO_TAIL_CALL 1
 #define ABSL_ATTRIBUTE_NO_TAIL_CALL \
   __attribute__((optimize("no-optimize-sibling-calls")))

absl/debugging/internal/examine_stack.cc

@@ -66,6 +66,8 @@ void* GetProgramCounter(void* vuc) {
 #elif defined(__x86_64__)
     if (16 < ABSL_ARRAYSIZE(context->uc_mcontext.gregs))
       return reinterpret_cast<void*>(context->uc_mcontext.gregs[16]);
+#elif defined(__e2k__)
+    return reinterpret_cast<void*>(context->uc_mcontext.cr0_hi);
 #else
 #error "Undefined Architecture."
 #endif