Don't compile yarn sources when threading is disabled in pigz CMake.

test/pigz/CMakeLists.txt

@@ -43,8 +43,11 @@ elseif(CMAKE_C_COMPILER_ID STREQUAL "GNU")
     if(NOT CMAKE_C_COMPILER_VERSION VERSION_LESS 4.8.0)
         add_definitions(-fno-diagnostics-show-caret)
     endif()
-elseif(MSVC)
-    add_definitions(-D_CRT_SECURE_NO_DEPRECATE)
+elseif(WIN32)
+    add_definitions(-D_TIMESPEC_DEFINED)
+    if(MSVC)
+        add_definitions(-D_CRT_SECURE_NO_DEPRECATE)
+    endif()
 endif()
 
 # Fetch pigz source code from official repository
@@ -59,21 +62,17 @@ endif()
 
 set(PIGZ_SRCS
     ${pigz_SOURCE_DIR}/pigz.c
-    ${pigz_SOURCE_DIR}/try.c
-    ${pigz_SOURCE_DIR}/yarn.c)
+    ${pigz_SOURCE_DIR}/try.c)
 
 set(PIGZ_HDRS
-    ${pigz_SOURCE_DIR}/try.h
-    ${pigz_SOURCE_DIR}/yarn.h)
+    ${pigz_SOURCE_DIR}/try.h)
 
 add_executable(${PROJECT_NAME} ${PIGZ_SRCS} ${PIGZ_HDRS})
 add_definitions(-DNOZOPFLI)
 
+# Find and link against pthreads or pthreads4w
 if(WITH_THREADS)
-    # Find and link against pthreads or pthreads4w
     if(WIN32)
-        add_definitions(-D_TIMESPEC_DEFINED)
-
         if(DEFINED PTHREADS4W_ROOT)
             set(CLEANUP_STYLE VC)
             set(PTHREADS4W_VERSION 3)
@@ -82,7 +81,7 @@ if(WITH_THREADS)
             target_link_libraries(${PROJECT_NAME} pthreadVC3)
             target_include_directories(${PROJECT_NAME} PRIVATE win ${PTHREADS4W_ROOT})
         else()
-            message(WARNING "Missing pthreads4w root directory, disabling threading")
+            message(WARNING "Missing pthreads4w root directory")
             set(WITH_THREADS OFF)
         endif()
     else()
@@ -97,6 +96,9 @@ endif()
 # Disable threading support
 if(NOT WITH_THREADS)
     add_definitions(-DNOTHREAD)
+else()
+    set_property(TARGET ${PROJECT_NAME} PROPERTY SOURCES APPEND
+        ${pigz_SOURCE_DIR}/yarn.c ${pigz_SOURCE_DIR}/yarn.h)
 endif()
 
 # Find and link against zlib