[Bug] Use mremap() to allocate a dual mapped region on NetBSD

In addition, always enable DualMapping when RWX pages are not
possible to allocate in JitAllocator, because otherwise the
allocator would not be able to allocate memory for JIT code
execution.

New CI runners to test FreeBSD, NetBSD, and OpenBSD are also
provided.

.github/workflows/build.yml

@@ -149,3 +149,93 @@ jobs:
 
       - name: "Test"
         run: python build-actions/action.py --step=test
+
+  build-vm:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - { host: "macos-12", os: "freebsd", osver: "13.1", cc: "clang", arch: "x86-64", build_type: "Release", defs: "ASMJIT_TEST=ON" }
+          - { host: "macos-12", os: "openbsd", osver: "7.2" , cc: "clang", arch: "x86-64", build_type: "Release", defs: "ASMJIT_TEST=ON" }
+
+    name: "${{matrix.os}}-${{matrix.osver}} (${{matrix.cc}}, ${{matrix.arch}}, ${{matrix.build_type}})"
+    runs-on: ${{matrix.host}}
+
+    steps:
+      - name: "Checkout"
+        uses: actions/checkout@v3
+        with:
+          path: "source"
+
+      - name: "Checkout Build Actions"
+        uses: actions/checkout@v3
+        with:
+          repository: build-actions/build-actions
+          path: "build-actions"
+
+      - name: Build & Test in VM
+        uses: cross-platform-actions/action@master
+        with:
+          operating_system: ${{matrix.os}}
+          architecture: ${{matrix.arch}}
+          version: ${{matrix.osver}}
+          shell: bash
+          run: |
+            set -e
+
+            PATH="/usr/sbin:/usr/pkg/sbin:/usr/pkg/bin:$PATH:$(pwd)/build-actions"
+            export PATH
+
+            sh ./build-actions/install-python3.sh
+            python3 build-actions/action.py                       \
+              --step=all                                          \
+              --compiler=${{matrix.cc}}                           \
+              --architecture=${{matrix.arch}}                     \
+              --source-dir=source                                 \
+              --config=source/.github/workflows/build-config.json \
+              --build-type=${{matrix.build_type}}                 \
+              --build-defs=${{matrix.defs}}
+
+  build-netbsd:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - { title: "netbsd", host: "macos-12", os: "netbsd", cc: "clang", arch: "x86_64", build_type: "Release", defs: "ASMJIT_TEST=ON" }
+
+    name: "${{matrix.title}} (${{matrix.cc}}, ${{matrix.arch}}, ${{matrix.build_type}})"
+    runs-on: ${{matrix.host}}
+
+    steps:
+      - name: "Checkout"
+        uses: actions/checkout@v3
+        with:
+          path: "source"
+
+      - name: "Checkout Build Actions"
+        uses: actions/checkout@v3
+        with:
+          repository: build-actions/build-actions
+          path: "build-actions"
+
+      - name: Build & Test (VM)
+        uses: vmactions/netbsd-vm@v0
+        with:
+          mem: 6144
+          usesh: true
+          copyback: false
+          run: |
+            set -e
+
+            PATH="/usr/sbin:/usr/pkg/sbin:/usr/pkg/bin:$PATH:$(pwd)/build-actions"
+            export PATH
+
+            bash ./build-actions/install-python3.sh
+            python3 ./build-actions/action.py                     \
+              --step=all                                          \
+              --compiler=${{matrix.cc}}                           \
+              --architecture=${{matrix.arch}}                     \
+              --source-dir=source                                 \
+              --config=source/.github/workflows/build-config.json \
+              --build-type=${{matrix.build_type}}                 \
+              --build-defs=${{matrix.defs}}