tcg: fix --disable-tcg build breakage

Fix the --disable-tcg breakage introduced by tb_lock's removal by
relying on the fact that tcg_enabled() is set to 0 at
compile-time under --disable-tcg.

While at it, add further asserts to fix builds that enable both
--disable-tcg and --enable-debug, which were broken even before
tb_lock's removal.

Tested to build x86_64-softmmu and i386-softmmu targets.

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

accel/stubs/tcg-stub.c

@@ -21,10 +21,6 @@ void tb_flush(CPUState *cpu)
 {
 }
 
-void tb_unlock(void)
-{
-}
-
 void tlb_set_dirty(CPUState *cpu, target_ulong vaddr)
 {
 }

cpus.c

@@ -1355,6 +1355,7 @@ static int tcg_cpu_exec(CPUState *cpu)
     int64_t ti;
 #endif
 
+    assert(tcg_enabled());
 #ifdef CONFIG_PROFILER
     ti = profile_getclock();
 #endif
@@ -1397,6 +1398,7 @@ static void *qemu_tcg_rr_cpu_thread_fn(void *arg)
 {
     CPUState *cpu = arg;
 
+    assert(tcg_enabled());
     rcu_register_thread();
     tcg_register_thread();
 
@@ -1631,6 +1633,7 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
 {
     CPUState *cpu = arg;
 
+    assert(tcg_enabled());
     g_assert(!use_icount);
 
     rcu_register_thread();
@@ -1854,6 +1857,7 @@ static void qemu_tcg_init_vcpu(CPUState *cpu)
     static QemuThread *single_tcg_cpu_thread;
     static int tcg_region_inited;
 
+    assert(tcg_enabled());
     /*
      * Initialize TCG regions--once. Now is a good time, because:
      * (1) TCG's init context, prologue and target globals have been set up.

exec.c

@@ -1323,6 +1323,7 @@ static void tlb_reset_dirty_range_all(ram_addr_t start, ram_addr_t length)
     RAMBlock *block;
     ram_addr_t end;
 
+    assert(tcg_enabled());
     end = TARGET_PAGE_ALIGN(start + length);
     start &= TARGET_PAGE_MASK;
 
@@ -2655,6 +2656,7 @@ void memory_notdirty_write_prepare(NotDirtyInfo *ndi,
 void memory_notdirty_write_complete(NotDirtyInfo *ndi)
 {
     if (ndi->pages) {
+        assert(tcg_enabled());
         page_collection_unlock(ndi->pages);
         ndi->pages = NULL;
     }
@@ -3046,6 +3048,7 @@ static void tcg_commit(MemoryListener *listener)
     CPUAddressSpace *cpuas;
     AddressSpaceDispatch *d;
 
+    assert(tcg_enabled());
     /* since each CPU stores ram addresses in its TLB cache, we must
        reset the modified entries */
     cpuas = container_of(listener, CPUAddressSpace, tcg_as_listener);