build-openmp: Build the OpenMP library on all architectures

Since a356782426f5bf54a00570e1f925345e5fda7b2e in llvm-project,
OpenMP can be built for mingw/aarch64, since
fb947c358661b3bd3d5e1fa776ec74cc0f308854 it should work correctly
in all currently tested cases, and since
97958c9bb83cec44b6ce13e732b53de0171a5d43 it can be built for
mingw/armv7.

run-tests.sh

@@ -114,14 +114,14 @@ for arch in $ARCHS; do
         COPY="$COPY_ARMV7"
         NATIVE="$NATIVE_ARMV7"
         unset HAVE_SANITIZERS
-        unset HAVE_OPENMP
+        HAVE_OPENMP=1
         ;;
     aarch64)
         RUN="$RUN_AARCH64"
         COPY="$COPY_AARCH64"
         NATIVE="$NATIVE_AARCH64"
         unset HAVE_SANITIZERS
-        unset HAVE_OPENMP
+        HAVE_OPENMP=1
         ;;
     esac