Add branch instructions to Subzero bitcode reader.

tests_lit/reader_tests/branch.ll

+; Tests if we handle a branch instructions.
+
+; RUN: llvm-as < %s | pnacl-freeze \
+; RUN:              | %llvm2ice -notranslate -verbose=inst -build-on-read \
+; RUN:                -allow-pnacl-reader-error-recovery \
+; RUN:              | FileCheck %s
+
+define void @SimpleBranch() {
+  br label %b3
+b1:
+  br label %b2
+b2:
+  ret void
+b3:
+  br label %b1
+}
+
+; CHECK:      define void @SimpleBranch() {
+; CHECK-NEXT: __0:
+; CHECK-NEXT:   br label %__3
+; CHECK-NEXT: __1:
+; CHECK-NEXT:   br label %__2
+; CHECK-NEXT: __2:
+; CHECK-NEXT:   ret void
+; CHECK-NEXT: __3:
+; CHECK-NEXT:   br label %__1
+; CHECK-NEXT: }
+
+define void @CondBranch(i32 %p) {
+  %test = trunc i32 %p to i1
+  br i1 %test, label %b1, label %b2
+b1:
+  ret void
+b2:
+  br i1 %test, label %b2, label %b1
+}
+
+; CHECK-NEXT: define void @CondBranch(i32 %__0) {
+; CHECK-NEXT: __0:
+; CHECK-NEXT:   %__1 = trunc i32 %__0 to i1
+; CHECK-NEXT:   br i1 %__1, label %__1, label %__2
+; CHECK-NEXT: __1:
+; CHECK-NEXT:   ret void
+; CHECK-NEXT: __2:
+; CHECK-NEXT:   br i1 %__1, label %__2, label %__1
+; CHECK-NEXT: }