Reduce stack usage for overflow checks

This reduces the stack space reserved for overflow checks to 12K, split
into an 8K gap and a 4K protected region.  GC needs over 8K when running
in a stack overflow situation.

Also prevents signal runaway by detecting a signal inside code that
resulted from a signal handler invokation.  And adds a max signal count to
the SignalTest to prevent it running forever.

Also reduces the number of iterations for the InterfaceTest as this was
taking (almost) forever with the --trace option on run-test.

Bug: 15435566

Change-Id: Id4fd46f22d52d42a9eb431ca07948673e8fda694
diff --git a/runtime/instruction_set.cc b/runtime/instruction_set.cc
index d7e358c..d8a38f4 100644
--- a/runtime/instruction_set.cc
+++ b/runtime/instruction_set.cc
@@ -87,11 +87,10 @@
 static constexpr size_t kDefaultStackOverflowReservedBytes = 16 * KB;
 static constexpr size_t kMipsStackOverflowReservedBytes = kDefaultStackOverflowReservedBytes;
 
-// TODO: Lower once implicit stack-overflow checks can work with less than 16K.
-static constexpr size_t kArmStackOverflowReservedBytes =    (kIsDebugBuild ? 16 : 16) * KB;
-static constexpr size_t kArm64StackOverflowReservedBytes =  (kIsDebugBuild ? 16 : 16) * KB;
-static constexpr size_t kX86StackOverflowReservedBytes =    (kIsDebugBuild ? 16 : 16) * KB;
-static constexpr size_t kX86_64StackOverflowReservedBytes = (kIsDebugBuild ? 16 : 16) * KB;
+static constexpr size_t kArmStackOverflowReservedBytes =    8 * KB;
+static constexpr size_t kArm64StackOverflowReservedBytes =  8 * KB;
+static constexpr size_t kX86StackOverflowReservedBytes =    8 * KB;
+static constexpr size_t kX86_64StackOverflowReservedBytes = 8 * KB;
 
 size_t GetStackOverflowReservedBytes(InstructionSet isa) {
   switch (isa) {