meson: don't link pthreads when internal impl is used

meson.build

@@ -24,7 +24,6 @@ libswresample = dependency('libswresample', version: '>= 3.9.100')
 libswscale = dependency('libswscale', version: '>= 5.9.100')
 
 libass = dependency('libass', version: '>= 0.12.2')
-pthreads = dependency('threads')
 
 # the dependency order of libass -> ffmpeg is necessary due to
 # static linking symbol resolution between fontconfig and MinGW
@@ -34,8 +33,7 @@ dependencies = [libass,
                 libavformat,
                 libavutil,
                 libswresample,
-                libswscale,
+                libswscale]
-                pthreads]
 
 # Keeps track of all enabled/disabled features
 features = {
@@ -364,6 +362,11 @@ if features['win32-internal-pthreads']
     # Hack around it by using HAVE_WIN32_INTERNAL_PTHREADS.
     includedir += include_directories('osdep/win32/include')
     sources += files('osdep/win32/pthread.c')
+else
+    # pthreads is intentionally left undefined in win32 branch to find incorrect
+    # uses of it immediately
+    pthreads = dependency('threads')
+    dependencies += pthreads
 endif
 
 pthread_debug = get_option('pthread-debug').require(

test/meson.build

@@ -31,6 +31,9 @@ test_utils_files = [
     'ta/ta_talloc.c',
     'ta/ta_utils.c'
 ]
+
+test_utils_deps = [libavutil, libm]
+
 # The zimg code requires using threads. On windows, threads
 # also requires timer code so this is added.
 if features['win32-internal-pthreads']
@@ -39,9 +42,10 @@ if features['win32-internal-pthreads']
                          'osdep/timer-win2.c',
                          'osdep/win32/pthread.c',
                          'osdep/windows_utils.c']
+else
+    test_utils_deps += pthreads
 endif
 
-test_utils_deps = [libavutil, libm, pthreads]
 if features['win32-desktop']
     test_utils_deps += cc.find_library('winmm')
 endif