Ignore missing library dependencies in CMake

Signed-off-by: Marcin Serwin <marcin@serwin.dev>

CMakeLists.txt

@@ -616,11 +616,14 @@ set(LINKED_LIBS)
 if(MINIAUDIO_NO_RUNTIME_LINKING)
     is_backend_enabled(PULSEAUDIO)
     if (PULSEAUDIO_ENABLED)
-        find_package(PulseAudio REQUIRED)
+        find_package(PulseAudio)
+
+        if (PulseAudio_FOUND)
             target_link_libraries(miniaudio PRIVATE ${PULSEAUDIO_LIBRARY})
             target_include_directories(miniaudio SYSTEM PRIVATE ${PULSEAUDIO_INCLUDE_DIR})
             list(APPEND LINKED_LIBS libpulse)
         endif()
+    endif()
 
     is_backend_enabled(ALSA)
     if (ALSA_ENABLED)
@@ -634,6 +637,8 @@ if(MINIAUDIO_NO_RUNTIME_LINKING)
             NAMES asound
             HINTS ${PC_ALSA_LIBRARY_DIRS}
         )
+
+        if (ALSA_LIBRARY)
             find_path(ALSA_INCLUDE_DIR
                 NAMES alsa/asoundlib.h
                 HINTS ${PC_ALSA_INCLUDE_DIRS}
@@ -643,6 +648,7 @@ if(MINIAUDIO_NO_RUNTIME_LINKING)
             target_include_directories(miniaudio PRIVATE ${ALSA_INCLUDE_DIR})
             list(APPEND LINKED_LIBS alsa)
         endif()
+    endif()
 
     is_backend_enabled(SNDIO)
     if (SNDIO_ENABLED)
@@ -656,9 +662,12 @@ if(MINIAUDIO_NO_RUNTIME_LINKING)
             NAMES sndio
             HINTS ${PC_SNDIO_LIBRARY_DIRS}
         )
+
+        if (SNDIO_LIBRARY)
             target_link_libraries(miniaudio PRIVATE ${SNDIO_LIBRARY})
             list(APPEND LINKED_LIBS sndio)
         endif()
+    endif()
 
     is_backend_enabled(JACK)
     if (JACK_ENABLED)
@@ -673,6 +682,7 @@ if(MINIAUDIO_NO_RUNTIME_LINKING)
             HINTS ${PC_JACK_LIBRARY_DIRS}
         )
 
+        if (JACK_LIBRARY)
             find_path(JACK_INCLUDE_DIR
                 NAMES jack/jack.h
                 HINTS ${PC_JACK_INCLUDE_DIRS}
@@ -683,6 +693,7 @@ if(MINIAUDIO_NO_RUNTIME_LINKING)
             list(APPEND LINKED_LIBS jack)
         endif()
     endif()
+endif()
 
 # Tests
 #