ci: Bump minimal compilers versions

Require GCC 11 (previously 10) and Clang 13 (previously 11).
Earlier versions do not have good C++20 support, in particular
the `using enum` feature.

Add xcode-min with Xcode 13.4.1 job to monitor minimal version required.

circle.yml

@@ -32,7 +32,7 @@ executors:
       CMAKE_BUILD_PARALLEL_LEVEL: 8
   linux-gcc-min:
     docker:
-      - image: ethereum/cpp-build-env:15-gcc-10
+      - image: ethereum/cpp-build-env:17-gcc-11
     resource_class: small
     environment:
       CMAKE_BUILD_PARALLEL_LEVEL: 2
@@ -43,7 +43,7 @@ executors:
       CMAKE_BUILD_PARALLEL_LEVEL: 4
   linux-clang-min:
     docker:
-      - image: ethereum/cpp-build-env:16-clang-11
+      - image: ethereum/cpp-build-env:18-clang-13
     resource_class: small
     environment:
       CMAKE_BUILD_PARALLEL_LEVEL: 2
@@ -57,7 +57,12 @@ executors:
     macos:
       xcode: 14.1.0
     environment:
-      CMAKE_BUILD_PARALLEL_LEVEL: 2
+      CMAKE_BUILD_PARALLEL_LEVEL: 4
+  macos-xcode-min:
+    macos:
+      xcode: 13.4.1
+    environment:
+      CMAKE_BUILD_PARALLEL_LEVEL: 4
 
 commands:
   install_cmake:
@@ -474,6 +479,15 @@ jobs:
       - build
       - test
 
+  xcode-min:
+    executor: macos-xcode-min
+    steps:
+      - run:
+          name: "Install System Dependencies"
+          command: HOMEBREW_NO_AUTO_UPDATE=1 brew install cmake
+      - build
+      - test
+
   cmake-min:
     executor: linux-base
     steps:
@@ -516,5 +530,6 @@ workflows:
       - clang-latest-sanitizers
       - clang-latest-coverage
       - macos-asan
+      - xcode-min
       - gcc-32bit
       - fuzzing