PPC/s390: [test] Add cctest for i-cache coherency assumptions.

Port fed7bb50

Original Commit Message:

    This test cases ensures that it is possible to maintain a coherent
    instruction cache by using {Assembler::FlushICache} in any order with
    respect to changing page permissions via {SetPermissions}.

R=mstarzinger@chromium.org, joransiu@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=v8:6792
LOG=N

Change-Id: I23d5d0828dcbdd527aaa8708fa726a7cb5cbedfe
Reviewed-on: https://chromium-review.googlesource.com/c/1347511Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#57745}

test/cctest/test-icache.cc

@@ -49,6 +49,14 @@ static void FloodWithInc(Isolate* isolate, byte* buffer, size_t allocated) {
   for (int i = 0; i < kNumInstr; ++i) {
     __ Addu(v0, v0, Operand(1));
   }
+#elif V8_TARGET_ARCH_PPC
+  for (int i = 0; i < kNumInstr; ++i) {
+    __ addi(r3, r3, Operand(1));
+  }
+#elif V8_TARGET_ARCH_S390
+  for (int i = 0; i < kNumInstr; ++i) {
+    __ agfi(r2, Operand(1));
+  }
 #else
 #error Unsupported architecture
 #endif