fix qtfred heap corruption in FastDebug builds (scp-fs2open#7450)

FastDebug FSO compiled with /MDd (debug CRT) but imported Qt's Release
libraries via CMAKE_MAP_IMPORTED_CONFIG_FASTDEBUG = Release Debug. Qt
Release ships /MD, so any allocation crossing the qtfred <-> Qt boundary
went into one heap and came back out of the other, tripping
_CrtIsValidHeapPointer on a perfectly-valid std::string dtor. Latent for
ages because it only surfaces when an allocation actually crosses;
opening a mission file is one such path.

To paper over the resulting STL layout difference, FastDebug also forced
_ITERATOR_DEBUG_LEVEL=0 so qtfred's std::string matched Release Qt's.
Not needed once we link Debug Qt, and keeping it would introduce a fresh
mismatch (qtfred IDL=0 vs Debug Qt IDL=2).

Fix:
  - Map FastDebug imports to "Debug Release \"\"" in qtfred/CMakeLists.
    Debug picks Qt's debug libs; Release is a defensive fallback; the
    empty entry falls back to plain IMPORTED_LOCATION, required because
    Qt's host tools (uic/moc/rcc/qhelpgenerator) ship a single variant
    with no IMPORTED_LOCATION_<CONFIG>. Must precede find_package(Qt5):
    CMake snapshots the variable into each target's MAP_IMPORTED_CONFIG
    property at creation time. (Also why the prior "Release Debug" was
    silently a no-op -- set after find_package, ignored; CMake fell
    back to Release on its own.)
  - Extend the qwindows/qsqlite plugin POST_BUILD copies' "d"-suffix
    generator expression to match FastDebug as well as Debug, so the
    Debug Qt runtime finds qwindowsd.dll / qsqlited.dll alongside.
  - Drop the FastDebug-only _ITERATOR_DEBUG_LEVEL=0 from the MSVC
    toolchain file. Qt was the sole consumer; pure-C deps don't care.

Cost: FastDebug STL containers pick up MSVC's debug-iterator overhead.
Reasonable trade for a config named "Debug with optimizations".

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Goober5000

cmake/toolchain-msvc.cmake

@@ -114,7 +114,6 @@ if(IS_X86)
 
 endif()
 
-add_compile_definitions("$<$<CONFIG:FastDebug>:_ITERATOR_DEBUG_LEVEL=0>")
 target_compile_definitions(compiler INTERFACE _CRT_SECURE_NO_DEPRECATE _CRT_SECURE_NO_WARNINGS _SECURE_SCL=0 NOMINMAX _SILENCE_TR1_NAMESPACE_DEPRECATION_WARNING)
 
 if (FSO_FATAL_WARNINGS)

qtfred/CMakeLists.txt

@@ -8,6 +8,18 @@ SET(QT5_INSTALL_ROOT "" CACHE PATH
 
 list(APPEND CMAKE_PREFIX_PATH "${QT5_INSTALL_ROOT}")
 
+# Must be set before find_package -- CMake snapshots this into each imported target's
+# MAP_IMPORTED_CONFIG_FASTDEBUG property at target-creation time, not at link time.
+# The list entries are tried in order:
+#   "Debug"   -- matches the per-config IMPORTED_LOCATION_DEBUG on Qt's libraries.
+#   "Release" -- per-config fallback if any target ships only a Release variant.
+#   ""        -- the empty entry means "fall back to the suffix-less IMPORTED_LOCATION".
+#                Required because Qt's host tools (uic/moc/rcc/qhelpgenerator) set
+#                only IMPORTED_LOCATION (no IMPORTED_CONFIGURATIONS), so without this
+#                CMake errors with "IMPORTED_LOCATION not set for imported target
+#                Qt5::uic configuration FastDebug".
+set(CMAKE_MAP_IMPORTED_CONFIG_FASTDEBUG Debug Release "")
+
 find_package(Qt5 COMPONENTS Widgets OpenGL Help REQUIRED)
 
 include(source_groups.cmake)
@@ -51,8 +63,6 @@ if(WIN32)
     set_property(TARGET qtfred PROPERTY QT5_NO_LINK_QTMAIN ON)
 endif()
 
-set(CMAKE_MAP_IMPORTED_CONFIG_FASTDEBUG Release Debug)
-
 target_link_libraries(qtfred
     PUBLIC
     code
@@ -169,11 +179,11 @@ if (WIN32)
 
     # Windows requires that the qwindows DLL is copied as well
     execute_process(COMMAND ${QT_QMAKE_EXECUTABLE} -query QT_INSTALL_PLUGINS OUTPUT_VARIABLE QT_INSTALL_PLUGINS OUTPUT_STRIP_TRAILING_WHITESPACE)
-    set(qwindows_path "${QT_INSTALL_PLUGINS}/platforms/qwindows$<$<CONFIG:Debug>:d>.dll")
+    set(qwindows_path "${QT_INSTALL_PLUGINS}/platforms/qwindows$<$<OR:$<CONFIG:Debug>,$<CONFIG:FastDebug>>:d>.dll")
 
     add_custom_command(TARGET qtfred
         POST_BUILD
-        COMMAND ${CMAKE_COMMAND} -E copy_if_different "${qwindows_path}" "$<TARGET_FILE_DIR:qtfred>/platforms/qwindows$<$<CONFIG:Debug>:d>.dll"
+        COMMAND ${CMAKE_COMMAND} -E copy_if_different "${qwindows_path}" "$<TARGET_FILE_DIR:qtfred>/platforms/qwindows$<$<OR:$<CONFIG:Debug>,$<CONFIG:FastDebug>>:d>.dll"
     VERBATIM)
 
     install(FILES ${qwindows_path}
@@ -182,11 +192,11 @@ if (WIN32)
     )
 
     # Qt Help requires the SQLite SQL driver
-    set(qsqlite_path "${QT_INSTALL_PLUGINS}/sqldrivers/qsqlite$<$<CONFIG:Debug>:d>.dll")
+    set(qsqlite_path "${QT_INSTALL_PLUGINS}/sqldrivers/qsqlite$<$<OR:$<CONFIG:Debug>,$<CONFIG:FastDebug>>:d>.dll")
 
     add_custom_command(TARGET qtfred
         POST_BUILD
-        COMMAND ${CMAKE_COMMAND} -E copy_if_different "${qsqlite_path}" "$<TARGET_FILE_DIR:qtfred>/sqldrivers/qsqlite$<$<CONFIG:Debug>:d>.dll"
+        COMMAND ${CMAKE_COMMAND} -E copy_if_different "${qsqlite_path}" "$<TARGET_FILE_DIR:qtfred>/sqldrivers/qsqlite$<$<OR:$<CONFIG:Debug>,$<CONFIG:FastDebug>>:d>.dll"
     VERBATIM)
 
     install(FILES ${qsqlite_path}