updating configure

configure

@@ -3249,22 +3249,20 @@ mkdir -p "${BUILDDIR}"
 owd=$(pwd)
 cd "${BUILDDIR}"
 
-cat <<EOF > test-omp.cpp
+# The configure script:
+cat > test-omp.cpp <<EOF
 #include <omp.h>
-int main() {
-  return omp_get_num_threads();
+extern "C" void configtest(int * arg) {
+  *arg = omp_get_num_threads();
 }
 EOF
-
-## Execute R CMD SHLIB.
-if ${CC} ${CFLAGS} -fopenmp test-omp.cpp >/dev/null 2>&1; then
-    { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
-printf "%s\n" "yes" >&6; }
-    openmp_already_works="yes"
-else
-    { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
-printf "%s\n" "no" >&6; }
-fi
+# Without the following you're relying on the GNU/Linux-like behaviour
+# w.r.t. undefined symbols (see WRE 1.2.1.1):
+cat > Makevars <<EOF
+PKG_CXXFLAGS = \$(SHLIB_OPENMP_CXXFLAGS)
+PKG_LIBS = \$(SHLIB_OPENMP_CXXFLAGS)
+EOF
+R CMD SHLIB test-omp.cpp
 
 ## Go back home.
 cd "${owd}"

configure.ac

@@ -46,20 +46,20 @@ mkdir -p "${BUILDDIR}"
 owd=$(pwd)
 cd "${BUILDDIR}"
 
-cat <<EOF > test-omp.cpp
+# The configure script:
+cat > test-omp.cpp <<EOF
 #include <omp.h>
-int main() {
-  return omp_get_num_threads();
+extern "C" void configtest(int * arg) {
+  *arg = omp_get_num_threads();
 }
 EOF
-
-## Execute R CMD SHLIB.
-if ${CC} ${CFLAGS} -fopenmp test-omp.cpp >/dev/null 2>&1; then
-    AC_MSG_RESULT([yes])
-    openmp_already_works="yes"
-else
-    AC_MSG_RESULT([no])
-fi
+# Without the following you're relying on the GNU/Linux-like behaviour
+# w.r.t. undefined symbols (see WRE 1.2.1.1):
+cat > Makevars <<EOF
+PKG_CXXFLAGS = \$(SHLIB_OPENMP_CXXFLAGS)
+PKG_LIBS = \$(SHLIB_OPENMP_CXXFLAGS)
+EOF
+R CMD SHLIB test-omp.cpp
 
 ## Go back home.
 cd "${owd}"