Don't erase things for BMC if function call is staticcall

test/libsolidity/smtCheckerTests/bmc_coverage/call_balance.sol

@@ -0,0 +1,13 @@
+contract C {
+	function f(address _a) public {
+		uint b1 = address(this).balance;
+		_a.call("");
+		uint b2 = address(this).balance;
+		assert(b1 == b2); // should fail
+	}
+}
+// ====
+// SMTEngine: bmc
+// ----
+// Warning 9302: (83-94): Return value of low-level calls not used.
+// Warning 4661: (133-149): BMC: Assertion violation happens here.

test/libsolidity/smtCheckerTests/bmc_coverage/call_state_var.sol

@@ -0,0 +1,13 @@
+contract C {
+	uint x;
+	function f(address _a) public {
+		x = 2;
+		_a.call("");
+		assert(x == 2); // should fail
+	}
+}
+// ====
+// SMTEngine: bmc
+// ----
+// Warning 9302: (66-77): Return value of low-level calls not used.
+// Warning 4661: (81-95): BMC: Assertion violation happens here.

test/libsolidity/smtCheckerTests/bmc_coverage/staticcall_balance.sol

@@ -0,0 +1,12 @@
+contract C {
+	function f(address _a) public view {
+		uint b1 = address(this).balance;
+		_a.staticcall("");
+		uint b2 = address(this).balance;
+		assert(b1 == b2); // should hold
+	}
+}
+// ====
+// SMTEngine: bmc
+// ----
+// Warning 9302: (88-105): Return value of low-level calls not used.

test/libsolidity/smtCheckerTests/bmc_coverage/staticcall_state_var.sol

@@ -0,0 +1,12 @@
+contract C {
+	uint x;
+	function f(address _a) public {
+		x = 2;
+		_a.staticcall("");
+		assert(x == 2); // should hold
+	}
+}
+// ====
+// SMTEngine: bmc
+// ----
+// Warning 9302: (66-83): Return value of low-level calls not used.