[tobil4sk]

Fix adapted from #1420

Not handling the cases correctly here could lead to stale objects failing to rebuild when adding flags. For example rebuilding a project with -D HXCPP_DEBUGGER caused:

/usr/bin/ld: obj/linux64/da3c452f_Debug.o: in function `__hxcpp_execution_trace(int)':
Debug.cpp:(.text+0x310): multiple definition of `__hxcpp_execution_trace(int)'; obj/linux64/da3c452f_Debugger.o:Debugger.cpp:(.text+0x2af0): first defined here
/usr/bin/ld: obj/linux64/da3c452f_Debug.o: in function `__hxcpp_set_debugger_info(char const**, char const**)':
Debug.cpp:(.text+0x540): multiple definition of `__hxcpp_set_debugger_info(char const**, char const**)'; obj/linux64/da3c452f_Debugger.o:Debugger.cpp:(.text+0x2b30): first defined here
/usr/bin/ld: obj/linux64/aea44ed0_Std.o: in function `Std_obj::isOfType(Dynamic, Dynamic)':
Std.cpp:(.text+0x767): undefined reference to `hx::ExceptionStackFrame::ExceptionStackFrame(hx::StackFrame const&)'
/usr/bin/ld: Std.cpp:(.text+0x7a4): undefined reference to `hx::StackContext::tracePosition()'
/usr/bin/ld: obj/linux64/aea44ed0_Std.o: in function `Std_obj::is(Dynamic, Dynamic)':
Std.cpp:(.text+0xa27): undefined reference to `hx::ExceptionStackFrame::ExceptionStackFrame(hx::StackFrame const&)'
/usr/bin/ld: Std.cpp:(.text+0xa64): undefined reference to `hx::StackContext::tracePosition()'
/usr/bin/ld: obj/linux64/aea44ed0_Std.o: in function `Std_obj::downcast(Dynamic, hx::ObjectPtr<hx::Class_obj>)':
Std.cpp:(.text+0xd67): undefined reference to `hx::ExceptionStackFrame::ExceptionStackFrame(hx::StackFrame const&)'
/usr/bin/ld: Std.cpp:(.text+0xd9c): undefined reference to `hx::StackContext::tracePosition()'
/usr/bin/ld: obj/linux64/aea44ed0_Std.o: in function `Std_obj::instance(Dynamic, hx::ObjectPtr<hx::Class_obj>)':
Std.cpp:(.text+0x10a7): undefined reference to `hx::ExceptionStackFrame::ExceptionStackFrame(hx::StackFrame const&)'
/usr/bin/ld: Std.cpp:(.text+0x10dc): undefined reference to `hx::StackContext::tracePosition()'
/usr/bin/ld: obj/linux64/aea44ed0_Std.o: in function `Std_obj::string(Dynamic)':
Std.cpp:(.text+0x1354): undefined reference to `hx::StackContext::tracePosition()'
/usr/bin/ld: Std.cpp:(.text+0x1397): undefined reference to `hx::ExceptionStackFrame::ExceptionStackFrame(hx::StackFrame const&)'
/usr/bin/ld: obj/linux64/aea44ed0_Std.o: in function `Std_obj::_hx_int(double)':
Std.cpp:(.text+0x1650): undefined reference to `hx::ExceptionStackFrame::ExceptionStackFrame(hx::StackFrame const&)'
/usr/bin/ld: Std.cpp:(.text+0x168c): undefined reference to `hx::StackContext::tracePosition()'
/usr/bin/ld: obj/linux64/aea44ed0_Std.o: in function `Std_obj::parseInt(String)':
Std.cpp:(.text+0x1917): undefined reference to `hx::ExceptionStackFrame::ExceptionStackFrame(hx::StackFrame const&)'
/usr/bin/ld: Std.cpp:(.text+0x1954): undefined reference to `hx::StackContext::tracePosition()'
/usr/bin/ld: obj/linux64/aea44ed0_Std.o: in function `Std_obj::parseFloat(String)':
Std.cpp:(.text+0x1bb5): undefined reference to `hx::ExceptionStackFrame::ExceptionStackFrame(hx::StackFrame const&)'
/usr/bin/ld: Std.cpp:(.text+0x1bf4): undefined reference to `hx::StackContext::tracePosition()'
/usr/bin/ld: obj/linux64/aea44ed0_Std.o: in function `Std_obj::random(int)':
Std.cpp:(.text+0x1ea4): undefined reference to `hx::StackContext::tracePosition()'
/usr/bin/ld: Std.cpp:(.text+0x1eeb): undefined reference to `hx::ExceptionStackFrame::ExceptionStackFrame(hx::StackFrame const&)'
/usr/bin/ld: obj/linux64/aea44ed0_Std.o: in function `hx::StackContext::popFrame(hx::StackFrame*)':
Std.cpp:(.text._ZN2hx12StackContext8popFrameEPNS_10StackFrameE[_ZN2hx12StackContext8popFrameEPNS_10StackFrameE]+0x43): undefined reference to `hx::ExceptionStackFrame::ExceptionStackFrame(hx::StackFrame const&)'
/usr/bin/ld: obj/linux64/3a5324da_Main_Fields_.o: in function `_Main::Main_Fields__obj::main() [clone .cold]':
Main_Fields_.cpp:(.text.unlikely+0x19): undefined reference to `hx::ExceptionStackFrame::ExceptionStackFrame(hx::StackFrame const&)'
/usr/bin/ld: obj/linux64/3a5324da_Main_Fields_.o: in function `_Main::Main_Fields__obj::main()':
Main_Fields_.cpp:(.text.startup+0x112): undefined reference to `hx::ExceptionStackFrame::ExceptionStackFrame(hx::StackFrame const&)'
/usr/bin/ld: Main_Fields_.cpp:(.text.startup+0x146): undefined reference to `hx::StackContext::tracePosition()'
/usr/bin/ld: obj/linux64/da3c452f_Debugger.o: in function `__hxcpp_on_line_changed(hx::StackContext*)':
Debugger.cpp:(.text+0x2a0d): undefined reference to `hx::StackContext::tracePosition()'
/usr/bin/ld: obj/linux64/da3c452f_Debugger.o: in function `hx::Breakpoints::HandleBreakpoints(hx::StackContext*)':
Debugger.cpp:(.text._ZN2hx11Breakpoints17HandleBreakpointsEPNS_12StackContextE[_ZN2hx11Breakpoints17HandleBreakpointsEPNS_12StackContextE]+0x3a9): undefined reference to `hx::StackContext::tracePosition()'
collect2: error: ld returned 1 exit status
Error: Build failed

Closes #991.