build: use CMAKE_POSITION_INDEPENDENT_CODE instead of -fPIC (#21947)

It's simpler to let cmake figure out what flags to add to each platforms
to create position independent code rather than handling it ourselves.

Also remove code that sets POSITION_INDEPENDENT_CODE property on SHARED
and MODULE libraries, as it's already on by default.

cmake.deps/cmake/BuildLibvterm.cmake

@@ -9,10 +9,8 @@ if(WIN32)
       -DCMAKE_INSTALL_PREFIX=${DEPS_INSTALL_DIR}
       -DCMAKE_C_COMPILER=${CMAKE_C_COMPILER}
       -DCMAKE_GENERATOR_PLATFORM=${CMAKE_GENERATOR_PLATFORM}
-      -DCMAKE_GENERATOR=${CMAKE_GENERATOR})
-  if(NOT MSVC)
-    list(APPEND LIBVTERM_CONFIGURE_COMMAND "-DCMAKE_C_FLAGS:STRING=-fPIC")
-  endif()
+      -DCMAKE_GENERATOR=${CMAKE_GENERATOR}
+      -DCMAKE_POSITION_INDEPENDENT_CODE=ON)
   set(LIBVTERM_BUILD_COMMAND ${CMAKE_COMMAND} --build . --config $<CONFIG>)
   set(LIBVTERM_INSTALL_COMMAND ${CMAKE_COMMAND} --build . --target install --config $<CONFIG>)
 else()