Add support for running tests that are expected to fail

Also add should-fail tests that exercise const and decl
initializers

tests_errors/const-1.ispc

@@ -0,0 +1,6 @@
+// Can't pre-increment
+
+int func() {
+    const int x = 2;
+    ++x;
+}

tests_errors/const-2.ispc

@@ -0,0 +1,6 @@
+// Can't assign to type
+
+int func() {
+    const int x = 2;
+    x = 0;
+}

tests_errors/const-3.ispc

@@ -0,0 +1,9 @@
+// Can't assign to type
+
+struct Foo {
+    int x;
+};
+
+int func(const Foo f) {
+    f.x = 0;
+}

tests_errors/const-4.ispc

@@ -0,0 +1,9 @@
+// Can't assign to type
+
+struct Foo {
+    int x;
+};
+
+int func(const int f) {
+    f -= 2;
+}

tests_errors/const-5.ispc

@@ -0,0 +1,6 @@
+// Can't assign to type
+
+int func() {
+    const int a[10] = {1,2,3,4,5,6,7,8,9,10};
+    a[0] = 1;
+}

tests_errors/decl-1.ispc

@@ -0,0 +1,5 @@
+// requires 10 values; 11 provided
+
+int func() {
+    int a[10] = {1,2,3,4,5,6,7,8,9,10,11};
+}

tests_errors/decl-2.ispc

@@ -0,0 +1,5 @@
+// requires 12 values; 11 provided
+
+int func() {
+    int a[12] = {1,2,3,4,5,6,7,8,9,10,11};
+}

tests_errors/decl-3.ispc

@@ -0,0 +1,5 @@
+// Expression list initializers can't be used
+
+int func() {
+    int a = { 1 };
+}

tests_errors/decl-4.ispc

@@ -0,0 +1,5 @@
+// Can't declare an unsized array as a local variable without providing an initializer expression to set its size
+
+int func() {
+    int a[];
+}