Fixed --enabled-debug on Windows MSYS2

This fixes the prior logic that relies on the (*)curses library
and header existing in compiler-derived default locations
such as /usr/include, and /usr/lib. However, if the package manager
happens to not install them there, then they will not be found
and the check will fail.

Four scenarios:
1. `./configure` or `./configure --enable-debug=no` produce:
    (no mention of debugger; configure continues)

2. `./configure --enable-debug=wrong` produces:
    configure: error: --enable-debug=wrong was requested but the value "wrong" is invalid
    (terminates with exit code 1)

3. `./configure --enable-debug` produces:

    config.h:
    defines C_DEBUG 1

    With only ncurses library installed:

    configure: debugger was requested, finding curses library ...
    checking for NCURSES... yes
    configure: debugger enabled using the ncurses library

    Makefile:
    CPPFLAGS = ... -D_DEFAULT_SOURCE -D_XOPEN_SOURCE=600 -I/usr/local/ncurses ...
    LIBS = ...  -L/usr/local/ncurses -lncurses -ltinfo ...

    With only ncursesw installed:

    configure: debugger was requested, finding curses library ...
    checking for NCURSES... no
    checking for NCURSESW... yes
    configure: debugger enabled using the ncursesw library

    Makefile:
    CPPFLAGS = ... -I/opt/ncursesw ...
    LIBS = ... -L/opt/ncursesw -lncursesw ...

    With only pdcurses isntalled:

    configure: debugger was requested, finding curses library ...
    checking for NCURSES... no
    checking for NCURSESW... no
    checking for PDCURSES... yes
    configure: debugger enabled using the pdcurses library

    Makefile:
    CPPFLAGS = ... -I/usr/local/pdcurses ...
    LIBS = ...  -L/usr/local/pdcurses -lpdcurses -ltinfo ...

    Without any curses library installed:

    configure: debugger was requested, finding curses library ...
    checking for NCURSES... no
    checking for NCURSESW... no
    checking for PDCURSES... no
    configure: error: Package requirements were not met:
    <pkg-info prints info about missing package>
    (terminates with exit code 1)

4. `./configure --enable-debug=heavy` produces same as above, but:

    config.h:
    defines C_DEBUG 1
    defines C_HEAVY_DEBUG 1

    The configure message mentions heavy, for example:

    configure: debugger was requested, finding curses library ...
    checking for NCURSES... yes
    configure: debugger with heavy debugging enabled using the ncurses library

.github/workflows/config.yml

@@ -20,11 +20,9 @@ jobs:
           - name: Linux
             os: ubuntu-latest
             compiler: gcc
-
-        # Disabled temporarily due to https://github.com/dreamer/dosbox-staging/issues/86
-        # - configure_flags:  --enable-debug
-        # - configure_flags:  --enable-debug-heavy
         conf:
+          - configure_flags:  --enable-debug
+          - configure_flags:  --enable-debug=heavy
           - configure_flags:  --enable-alsa-midi
           - configure_flags:  --disable-core-inline
           - configure_flags:  --disable-dynamic-x86
@@ -56,7 +54,7 @@ jobs:
         id:    cache-msys2
         with:
           path: 'C:/tools/msys64'
-          key: msys2-GCC-64-${{ steps.get-date.outputs.date }}-1
+          key: msys2-GCC-64-${{ steps.get-date.outputs.date }}-2
 
       - name:  Install MSYS2 (Windows)
         if:    matrix.system.name == 'Windows' && steps.cache-msys2.outputs.cache-hit != 'true'
@@ -84,6 +82,12 @@ jobs:
         shell: python scripts\msys-bash.py {0}
         run:   scripts/build.sh -c ${{ matrix.system.compiler }} -t debug --bin-path /mingw64/bin ${{ matrix.conf.configure_flags }}
 
-      - name:  Build ${{ matrix.conf.configure_flags }} (non-Windows)
-        if:    matrix.system.name != 'Windows'
+      - name:  Build ${{ matrix.conf.configure_flags }} (macOS)
+        if:    matrix.system.name == 'macOS'
+        run:   |
+          export PKG_CONFIG_PATH="/usr/local/opt/ncurses/lib/pkgconfig:$PKG_CONFIG_PATH"
+          ./scripts/build.sh -c ${{ matrix.system.compiler }} -t debug ${{ matrix.conf.configure_flags }}
+
+      - name:  Build ${{ matrix.conf.configure_flags }} (Linux)
+        if:    matrix.system.name == 'Linux'
         run:   ./scripts/build.sh -c ${{ matrix.system.compiler }} -t debug ${{ matrix.conf.configure_flags }}