Try fork test on Cygwin and Linux only

seems to hang on at least ARMv8/Android as well

utest/CMakeLists.txt

@@ -16,13 +16,10 @@ else ()
   )
 endif ()
 
+# known to hang with the native Windows and Android threads
+# FIXME needs checking if this works on any of the other platforms
 if (NOT USE_OPENMP)
-if (NOT OS_WINDOWS)
-set(OpenBLAS_utest_src
-  ${OpenBLAS_utest_src}
-  test_fork.c
-  )
-elseif (OS_CYGWIN_NT)
+if (OS_CYGWIN_NT OR OS_LINUX)
 set(OpenBLAS_utest_src
   ${OpenBLAS_utest_src}
   test_fork.c

utest/Makefile

@@ -15,13 +15,11 @@ ifneq ($(NO_LAPACK), 1)
 #OBJS += test_potrs.o
 endif
 
+#this does not work with OpenMP nor with native Windows or Android threads
+# FIXME TBD if this works on OSX, SunOS, POWER and zarch
 ifndef USE_OPENMP
-ifndef OS_WINDOWS
+ifeq ($(OSNAME), $(filter $(OSNAME),Linux CYGWIN_NT))
 OBJS += test_fork.o
-else
-ifdef OS_CYGWIN_NT
-OBJS += test_fork.o
-endif
 endif
 endif