Implement CMake build system

This is a draft of a CMake build system. It doesn't yet include RVFI, JSON docs, formal stuff, etc.

.gitignore

@@ -6,4 +6,7 @@ _build/
 _sbuild/
 *.o
 *.a
-/z3_problems
+z3_problems
+
+# Typical CMake build directory.
+/build

CMakeLists.txt

@@ -0,0 +1,76 @@
+cmake_minimum_required(VERSION 3.22)
+
+project(sail_riscv)
+
+# Enable CTest
+enable_testing()
+
+# We technically require C++20 since the C generated by Sail - which we compile
+# as C++ - uses designated initialisers, a C++20 feature. However in practice
+# much older compilers support this feature so everything does work with C++17,
+# but you get lots of warnings on compilers that support C++20 if you use
+# this feature without -std=c++20.
+if (cxx_std_20 IN_LIST CMAKE_CXX_COMPILE_FEATURES)
+    set(CMAKE_CXX_STANDARD 20)
+else()
+    set(CMAKE_CXX_STANDARD 17)
+endif()
+set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
+
+# Export compile_commands.json for IDE support.
+set(CMAKE_EXPORT_COMPILE_COMMANDS TRUE)
+
+# Always use Position Independent Code. By default it is only used for
+# shared libraries (which require it), but you also need it for static
+# libraries if you link them into shared libraries.
+# Generally it just simplifies everything for a negligable performance cost.
+set(CMAKE_POSITION_INDEPENDENT_CODE TRUE)
+
+# Don't allow undefined symbols in shared libraries. This is generally a pain.
+if (UNIX)
+    set(CMAKE_SHARED_LINKER_FLAGS "-Wl,--no-undefined")
+endif()
+
+# Optional faster binary. Increases compilation time a lot though due to LTO.
+option(EXTRA_FAST "Enable aggressive optimisation flags (-march=native, -flto, etc)" FALSE)
+
+if (EXTRA_FAST)
+    include("cmake/extra_fast.cmake")
+endif()
+
+# Extra CMake files.
+set(CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules")
+
+# These are the main requirements.
+# Don't use `REQUIRED` so that we can print custom help messages.
+find_package(ZLIB)
+if (NOT ZLIB_FOUND)
+    message(FATAL_ERROR "Zlib not found. Try 'sudo apt install zlib1g-dev' or 'sudo dnf install zlib-devel'.")
+endif()
+
+find_package(GMP)
+if (NOT GMP_FOUND)
+    message(FATAL_ERROR "GMP not found. Try 'sudo apt install libgmp3-dev' or 'sudo dnf install gmp-devel'.")
+endif()
+
+find_program(SAIL_BIN "sail")
+if (NOT SAIL_BIN)
+    message(FATAL_ERROR "Sail not found. See README.md for installation instructions.")
+endif()
+
+set(ENABLED_ARCHITECTURES "rv32;rv64" CACHE STRING "Enabled architectures to build (rv32, rv64, rv32d, rv64f)" )
+
+# Softfloat support.
+add_subdirectory("dependencies/softfloat")
+
+# Sail C runtime.
+add_subdirectory("sail_runtime")
+
+# Sail model generated C code.
+add_subdirectory("model")
+
+# Emulator binary.
+add_subdirectory("emulator")
+
+# Old pre-compiled riscv-tests.
+add_subdirectory("test/riscv-tests")