[dis]engage_platform declarations mismatch with mingw crosscompiler

[mbeniamino]

Describe the bug
Using catch.hpp with mingw crosscompiler leads to compilation errors:

In file included from main.cpp:4:
single_include/catch2/catch.hpp:10755:5: error: no declaration matches ‘int Catch::FatalConditionHandler::engage_platform()’
10755 |     FatalConditionHandler::engage_platform() {}
      |     ^~~~~~~~~~~~~~~~~~~~~
In file included from main.cpp:4:
single_include/catch2/catch.hpp:8007:14: note: candidate is: ‘void Catch::FatalConditionHandler::engage_platform()’
 8007 |         void engage_platform();
      |              ^~~~~~~~~~~~~~~
single_include/catch2/catch.hpp:8001:11: note: ‘class Catch::FatalConditionHandler’ defined here
 8001 |     class FatalConditionHandler {
      |           ^~~~~~~~~~~~~~~~~~~~~
In file included from main.cpp:4:
single_include/catch2/catch.hpp:10756:5: error: no declaration matches ‘int Catch::FatalConditionHandler::disengage_platform()’
10756 |     FatalConditionHandler::disengage_platform() {}
      |     ^~~~~~~~~~~~~~~~~~~~~
In file included from main.cpp:4:
single_include/catch2/catch.hpp:8008:14: note: candidate is: ‘void Catch::FatalConditionHandler::disengage_platform()’
 8008 |         void disengage_platform();
      |              ^~~~~~~~~~~~~~~~~~
single_include/catch2/catch.hpp:8001:11: note: ‘class Catch::FatalConditionHandler’ defined here
 8001 |     class FatalConditionHandler {
      |           ^~~~~~~~~~~~~~~~~~~~~
main.cpp:6:5: error: redefinition of ‘int main(int, char**)’
    6 | int main(int argc, char* argv[]) {
      |     ^~~~
In file included from main.cpp:4:
single_include/catch2/catch.hpp:17502:5: note: ‘int main(int, char**)’ previously defined here
17502 | int main (int argc, char * argv[]) {
      |     ^~~~

Expected behavior
The program compiles without errors.

Reproduction steps
Basically it happens when neither windows exceptions nor posix signals are handled. Program to reproduce the bug even with standard g++:

#define CATCH_CONFIG_MAIN
#define CATCH_CONFIG_NO_WINDOWS_SEH
#define CATCH_CONFIG_NO_POSIX_SIGNALS
#include <catch2/catch.hpp>

int main(int argc, char* argv[]) {
    return 0;
}

Platform information:

• OS: Arch Linux
• Compiler+version: x86_64-w64-mingw32-g++ (GCC) 10.1.0
• Catch version: v2.13.5

Additional context
A PR will follow in few minutes.

[horenmar]

🤦 Thanks.