Catch runaway ARMConstantIslandPass even in -Asserts builds.

The pass is prone to looping, and it is better to crash than loop
forever, even in a -Asserts build.

<rdar://problem/10660175>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147806 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/ARM/ARMConstantIslandPass.cpp b/lib/Target/ARM/ARMConstantIslandPass.cpp
index b73acd1..36be230 100644
--- a/lib/Target/ARM/ARMConstantIslandPass.cpp
+++ b/lib/Target/ARM/ARMConstantIslandPass.cpp
@@ -435,7 +435,7 @@
     for (unsigned i = 0, e = CPUsers.size(); i != e; ++i)
       CPChange |= HandleConstantPoolUser(i);
     if (CPChange && ++NoCPIters > 30)
-      llvm_unreachable("Constant Island pass failed to converge!");
+      report_fatal_error("Constant Island pass failed to converge!");
     DEBUG(dumpBBs());
 
     // Clear NewWaterList now.  If we split a block for branches, it should
@@ -447,7 +447,7 @@
     for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i)
       BRChange |= FixUpImmediateBr(ImmBranches[i]);
     if (BRChange && ++NoBRIters > 30)
-      llvm_unreachable("Branch Fix Up pass failed to converge!");
+      report_fatal_error("Branch Fix Up pass failed to converge!");
     DEBUG(dumpBBs());
 
     if (!CPChange && !BRChange)