aedi: ability to avoid prefix addition to search paths

prefix directory may not be added to search path via -I ... and -L ... command line options
this helps to upgrade dependencies, so they won't use old header or library files

aedi/target/base.py

@@ -66,6 +66,7 @@ class BuildTarget(Target):
         self.environment = os.environ.copy()
         self.options = CommandLineOptions()
         self.multi_platform = True
+        self.search_prefix = True
 
     def configure(self, state: BuildState):
         os.makedirs(state.build_path, exist_ok=True)
@@ -75,21 +76,28 @@ class BuildTarget(Target):
             + os.pathsep + '/Applications/CMake.app/Contents/bin' \
             + os.pathsep + state.bin_path
 
-        if not state.xcode:
-            env['CC'] = state.c_compiler()
-            env['CXX'] = state.cxx_compiler()
+        if state.xcode:
+            return
 
-            for prefix in ('CPP', 'C', 'CXX', 'OBJC', 'OBJCXX'):
-                varname = f'{prefix}FLAGS'
+        env['CC'] = state.c_compiler()
+        env['CXX'] = state.cxx_compiler()
 
+        for prefix in ('CPP', 'C', 'CXX', 'OBJC', 'OBJCXX'):
+            varname = f'{prefix}FLAGS'
+
+            if self.search_prefix:
                 self._update_env(varname, f'-I{state.include_path}')
-                self._set_sdk(state, varname)
-                self._set_os_version(state, varname)
 
-            ldflags = 'LDFLAGS'
+            self._set_sdk(state, varname)
+            self._set_os_version(state, varname)
+
+        ldflags = 'LDFLAGS'
+
+        if self.search_prefix:
             self._update_env(ldflags, f'-L{state.lib_path}')
-            self._set_sdk(state, ldflags)
-            self._set_os_version(state, ldflags)
+
+        self._set_sdk(state, ldflags)
+        self._set_os_version(state, ldflags)
 
     def _update_env(self, name: str, value: str):
         env = self.environment