[Synth] Don't run LEC tests if z3/lec-jit is not provided, NFC

Author: uenoku

integration_test/circt-synth/balance-mux.mlir

@@ -1,3 +1,6 @@
+// REQUIRES: libz3
+// REQUIRES: circt-lec-jit
+
 // RUN: circt-opt %s --pass-pipeline='builtin.module(synth-print-longest-path-analysis, hw.module(comb-balance-mux{mux-chain-threshold=4}))' -o %t.mlir | FileCheck %s --check-prefix=DEPTH_BEFORE
 // RUN: circt-opt %t.mlir --pass-pipeline='builtin.module(synth-print-longest-path-analysis)' | FileCheck %s --check-prefix=DEPTH_AFTER
 // RUN: circt-lec %t.mlir %s -c1=priority_mux_18_depth -c2=priority_mux_18_depth --shared-libs=%libz3 | FileCheck %s --check-prefix=MUX18_LEC