v2.0.20 build fails with flag -DWITH_THREADING=OFF

[mzymon]

v2.0.20 build fails on my windows machine with flag -DWITH_THREADING=OFF due to changes related with introduction of lib/pthread_compat.h.
Defines was renamed to "COMPAT_" and functions are not changed in all required places causing build failure.
e.g. in file actions.c line 158 there is still "pthread_mutex_lock" instead of "COMPAT_pthread_mutex_lock"
Previous definitions of those functions from lib/dummypthread.h were deleted in v2.0.20.

[mzymon]

Created pull request with fix #3140

[ralight]

Sorry, I'm not sure how that happened. Thanks for the PR!