Fix error: undefined symbol art::instruction_set_details::GetStackOverflowReservedBytesFailure

When ART is built with ART_DEBUG_OPT_FLAG="-O0". Linker fails with the
errors:

ld.lld: error: undefined symbol:
art::instruction_set_details::GetStackOverflowReservedBytesFailure(char
const*)
>>> referenced by instruction_set.h:271
(art/libartbase/arch/instruction_set.h:271)

ld.lld: error: undefined symbol:
art::instruction_set_details::GetStackOverflowReservedBytesFailure(char
const*)
>>> referenced by instruction_set.h:274
(art/libartbase/arch/instruction_set.h:274)

This happens because GetStackOverflowReservedBytesFailure is declared in
art::instruction_set_details but it is not defined there.

This CL puts the definition of GetStackOverflowReservedBytesFailure into
the instruction_set_details namespace.

Follow-up to commit a9b2f7b097d2ce0c354a907748d5864775b32088.

Test: ART_DEBUG_OPT_FLAG="-O0" art/tools/buildbot-build.sh --target
Change-Id: I641d48fd0901292fa94a2c329ad7feea98a6962b
diff --git a/libartbase/arch/instruction_set.cc b/libartbase/arch/instruction_set.cc
index d47f936..8d4fbf4 100644
--- a/libartbase/arch/instruction_set.cc
+++ b/libartbase/arch/instruction_set.cc
@@ -133,11 +133,11 @@
 static_assert(ART_FRAME_SIZE_LIMIT < kX86_64StackOverflowReservedBytes,
               "Frame size limit too large");
 
-}  // namespace instruction_set_details
-
 NO_RETURN void GetStackOverflowReservedBytesFailure(const char* error_msg) {
   LOG(FATAL) << error_msg;
   UNREACHABLE();
 }
 
+}  // namespace instruction_set_details
+
 }  // namespace art