utest: test fork safety on OpenMP >= 5

In addition to testing fork safety on non-OpenMP builds, test it on
OpenMP >= 5.0, where we get the ability to release the locks at fork()
time.

Makefile.prebuild

@@ -55,6 +55,10 @@ ifeq ($(TARGET), C910V)
 TARGET_FLAGS = -march=rv64gcv0p7_zfh_xtheadc -mabi=lp64d
 endif
 
+ifeq ($(USE_OPENMP), 1)
+EXFLAGS += -fopenmp
+endif
+
 all: getarch_2nd
 	./getarch_2nd  0 >> $(TARGET_MAKE)
 	./getarch_2nd  1 >> $(TARGET_CONF)

getarch.c

@@ -1941,6 +1941,10 @@ printf("ELF_VERSION=2\n");
     printf("MAKEFLAGS += -j %d\n", get_num_cores());
 #endif
 
+#if defined(_OPENMP)
+    printf("OPENMP_VERSION = %d\n", _OPENMP);
+#endif
+
     break;
 
   case '1' : /* For config.h */

utest/Makefile

@@ -26,7 +26,7 @@ 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
 ifeq ($(OSNAME), $(filter $(OSNAME),Linux CYGWIN_NT))
-ifneq ($(USE_OPENMP), 1)
+ifeq ($(shell test x"$(USE_OPENMP)" -ne x1 -o $(OPENMP_VERSION) -ge 201811 && echo 1), 1)
 OBJS += test_fork.o
 endif
 OBJS += test_post_fork.o