Fix building on macOS.

It seems like Apple have killed the remaining bits of TR1. Thankfully,
all Apple systems we support now have a C++11 compiler so we can just
force that on macOS.

[skip alpine ci]
[skip irctest ci]
[skip ubuntu ci]
[skip windows ci]

.github/workflows/ci-macos.yml

@@ -9,7 +9,6 @@ jobs:
     if: "!contains(github.event.head_commit.message, '[skip macos ci]')"
     runs-on: macos-latest
     env:
-      CXXFLAGS: -std=${{ matrix.standard }} -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
       HOMEBREW_NO_AUTO_UPDATE: 1
       HOMEBREW_NO_INSTALL_CLEANUP: 1
       HOMEBREW_NO_INSTALLED_DEPENDENTS_CHECK: 1
@@ -17,6 +16,11 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      - name: Prepare the build environment
+        run: |
+          echo "CPPFLAGS=-I$(brew --prefix)/include" >> $GITHUB_ENV
+          echo "LDFLAGS=-L$(brew --prefix)/lib" >> $GITHUB_ENV
+
       - name: Install dependencies
         run: |
           brew update || true
@@ -39,9 +43,3 @@ jobs:
 
       - name: Run test-build
         run: ./tools/test-build c++
-    strategy:
-      fail-fast: false
-      matrix:
-        standard:
-          - gnu++98
-          - c++17

make/template/main.mk

@@ -101,6 +101,7 @@ ifeq ($(SYSTEM), solaris)
   LDLIBS += -lsocket -lnsl -lrt -lresolv
 endif
 ifeq ($(SYSTEM), darwin)
+  CXX += -std=c++11
   LDLIBS += -ldl
   CORELDFLAGS = -dynamic -bind_at_load -L.
   PICLDFLAGS = -fPIC -shared -twolevel_namespace -undefined dynamic_lookup