Refactor: Move to simple default builds

* Remove individual feature flags in favor of a single `KPXC_MINIMAL` flag that removes advanced features from the build. Basic features are no longer guarded by feature flags.
* Basic features: Auto-Type, Yubikey, KeeShare
* Advanced features include: Browser (and passkeys), SSH Agent, and Secret Service
* Networking, Documentation, and Update Checking remain as feature flags to accommodate various distro requirements.

This change also cleans up the main CMakeLists.txt by re-arranging some content and placing macros into a dedicated include file. The minimum CMake version was bumped to 3.16.0 to conform to our minimum Ubuntu support of Focal (20.04). This also allows us to default to C++20, we fall back to C++17 for Qt versions less than 5.15.0 due to lack of support.

Lastly this change removes the KEEPASSXC_BUILD_TYPE="PreRelease" which is never used. We only support "Snapshot" and "Release" now.

cmake/CompilerFlags.cmake

@@ -0,0 +1,65 @@
+#  Copyright (C) 2024 KeePassXC Team <team@keepassxc.org>
+#
+#  This program is free software: you can redistribute it and/or modify
+#  it under the terms of the GNU General Public License as published by
+#  the Free Software Foundation, either version 2 or (at your option)
+#  version 3 of the License.
+#
+#  This program is distributed in the hope that it will be useful,
+#  but WITHOUT ANY WARRANTY; without even the implied warranty of
+#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#  GNU General Public License for more details.
+#
+#  You should have received a copy of the GNU General Public License
+#  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+macro(add_gcc_compiler_cxxflags FLAGS)
+    if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_COMPILER_IS_CLANGXX)
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${FLAGS}")
+    endif()
+endmacro()
+
+macro(add_gcc_compiler_cflags FLAGS)
+    if(CMAKE_COMPILER_IS_GNUCC OR CMAKE_COMPILER_IS_CLANG)
+        set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${FLAGS}")
+    endif()
+endmacro()
+
+macro(add_gcc_compiler_flags FLAGS)
+    add_gcc_compiler_cxxflags("${FLAGS}")
+    add_gcc_compiler_cflags("${FLAGS}")
+endmacro()
+
+# Copies of above macros that first ensure the compiler understands a given flag
+# Because check_*_compiler_flag() sets -D with name, need to provide "safe" FLAGNAME
+macro(check_add_gcc_compiler_cxxflag FLAG FLAGNAME)
+    check_cxx_compiler_flag("${FLAG}" CXX_HAS${FLAGNAME})
+    if(CXX_HAS${FLAGNAME})
+        add_gcc_compiler_cxxflags("${FLAG}")
+    endif()
+endmacro()
+
+macro(check_add_gcc_compiler_cflag FLAG FLAGNAME)
+    check_c_compiler_flag("${FLAG}" CC_HAS${FLAGNAME})
+    if(CC_HAS${FLAGNAME})
+        add_gcc_compiler_cflags("${FLAG}")
+    endif()
+endmacro()
+
+# This is the "front-end" for the above macros
+# Optionally takes additional parameter(s) with language to check (currently "C" or "CXX")
+macro(check_add_gcc_compiler_flag FLAG)
+    string(REGEX REPLACE "[-=]" "_" FLAGNAME "${FLAG}")
+    set(check_lang_spec ${ARGN})
+    list(LENGTH check_lang_spec num_extra_args)
+    set(langs C CXX)
+    if(num_extra_args GREATER 0)
+        set(langs "${check_lang_spec}")
+    endif()
+    if("C" IN_LIST langs)
+        check_add_gcc_compiler_cflag("${FLAG}" "${FLAGNAME}")
+    endif()
+    if("CXX" IN_LIST langs)
+        check_add_gcc_compiler_cxxflag("${FLAG}" "${FLAGNAME}")
+    endif()
+endmacro()

cmake/compiler-checks/ptrace_deny_attach.cpp

@@ -0,0 +1,8 @@
+#include <sys/ptrace.h>
+#include <sys/types.h>
+
+int main()
+{
+    ptrace(PT_DENY_ATTACH, 0, 0, 0);
+    return 0;
+}