Add basic test for incsp optimisation

test/val/bug2748.c

@@ -0,0 +1,32 @@
+#include "unittest.h"
+
+int func(int expr)
+{
+   {
+      int i = 5;
+      return i;
+   }
+}
+
+static size_t c_sp_before, c_sp_after;
+
+TEST
+{
+    int a = 11;
+    int b;
+
+    __asm__("lda c_sp");
+    __asm__("ldx c_sp+1");
+    c_sp_before = __AX__;
+
+    b = func(a);
+
+    __asm__("lda c_sp");
+    __asm__("ldx c_sp+1");
+    c_sp_after = __AX__;
+
+    ASSERT_IsTrue(c_sp_before == c_sp_after, "Unexpected stack pointer");
+    ASSERT_IsTrue(b == 5, "Wrong value for b");
+    ASSERT_IsTrue(a == 11, "Wrong value for a");
+}
+ENDTEST