Update CMake minimum to 3.18

Errors with Ghidra repo FetchContent when using CMake less than this
version. FetchContent runs the patch step before update and so we lose
the patches, which can cause build errors.

CMake 3.15 can still be used if you specify your own Ghidra repo on the
command line.

.github/workflows/main.yml

@@ -45,7 +45,7 @@ jobs:
           graphviz
 
         # Minimum supported CMake version testing
-        curl -L "https://github.com/Kitware/CMake/releases/download/v3.15.0/cmake-3.15.0-Linux-$(uname -m).sh" -o /tmp/cmake-install.sh
+        curl -L "https://github.com/Kitware/CMake/releases/download/v3.18.0/cmake-3.18.0-Linux-$(uname -m).sh" -o /tmp/cmake-install.sh
         mkdir -p "${HOME}/.local"
         bash /tmp/cmake-install.sh --skip-license --exclude-subdir "--prefix=${HOME}/.local"
 

CMakeLists.txt

@@ -6,7 +6,7 @@
 # the LICENSE file found in the root directory of this source tree.
 #
 
-cmake_minimum_required(VERSION 3.15)
+cmake_minimum_required(VERSION 3.18)
 
 # Sets "library_root" variable for decompiler cpp root directory
 # Sets "ghidra_version" for numeric version number

README.md

@@ -19,7 +19,7 @@ This repository provides a CMake-based build project for SLEIGH so that it can b
 | Name | Version | Linux Package to Install | macOS Homebrew Package to Install |
 | ---- | ------- | ------------------------ | --------------------------------- |
 | [Git](https://git-scm.com/) | Latest | git | N/A |
-| [CMake](https://cmake.org/) | 3.21+ | cmake | cmake |
+| [CMake](https://cmake.org/) | 3.18+ | cmake | cmake |
 
 **NOTE**: This CMake project pulls the Ghidra source code from the internet during configuration. See the [note on Ghidra source code section](#note-on-ghidra-source-code) for more details.
 

cmake/modules/sleighCompile.cmake

@@ -6,7 +6,7 @@
 # the LICENSE file found in the root directory of this source tree.
 #
 
-cmake_minimum_required(VERSION 3.15)
+cmake_minimum_required(VERSION 3.18)
 
 # Takes the following required arguments:
 #