Reapply "Improve build system, etc..."

This reverts commit 705f529f55.

src/CMakeLists.txt

@@ -30,7 +30,8 @@ set(PMT_SOURCES
 )
 
 # Add pmt
-add_executable(pmt ${PMT_SOURCES})
+add_executable(pmt ${PMT_SOURCES}
+        functions/ShellFunction.cpp)
 add_executable(pmt_static ${PMT_SOURCES})
 
 # Set linker options

src/functions/ShellFunction.cpp

@@ -0,0 +1,16 @@
+/*
+Copyright 2025 Yağız Zengin
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+           http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+

src/functions/functions.hpp

@@ -175,6 +175,17 @@ public:
   [[nodiscard]] const char *name() const override;
 };
 
+class shellFunction final : public FunctionBase {
+public:
+  CLI::App *cmd = nullptr;
+
+  bool init(CLI::App &_app) override;
+  bool run() override;
+
+  [[nodiscard]] bool isUsed() const override;
+  [[nodiscard]] const char *name() const override;
+};
+
 } // namespace PartitionManager
 
 #endif // #ifndef FUNCTIONS_HPP