Prevent mutex lock fail even if --enable-debug
Prevent mutex lock fail even if --enable-debug

This PR intends to resolve #15227.

"configure --debug-enabled" enables "#ifdef DEBUG_LOCKORDER".
Then "lockdata" (in sync.cpp) will be initialized same as other
static objects.

But unfortunately, lockdata.push_lock() was called before its
initialization (via initializing signatureCache which is declared
in script/sigcache.cpp) on macOS.

This PR apply the "Construct On First Use Idiom" to "lockdata"
to prevent it.

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