Unity Build: Fix per-config sources in multi-config generators

Single-config generators already support unity builds with per-config
sources because they compute sources using `CMAKE_BUILD_TYPE` as the
configuration.  Each original source is either included in the unity
build source, or not.

Teach multi-config generators to compute the list of sources for
inclusion in unity builds using all configurations.  Previously they
only used the empty string as the configuration.  Each original source
may be included in some configurations, but not others.  Use
preprocessor conditions to guard their inclusion when necessary.

Fixes: #22892

1 files changed, 9 insertions, 0 deletions

diff --git a/Tests/RunCMake/UnityBuild/per_config_c_debug.c b/Tests/RunCMake/UnityBuild/per_config_c_debug.c
new file mode 100644
index 0000000..6d32ead
--- /dev/null
+++ b/Tests/RunCMake/UnityBuild/per_config_c_debug.c
@@ -0,0 +1,9 @@
+#ifndef CFG_DEBUG
+#  error "per_config_c_debug built without CFG_DEBUG"
+#endif
+#ifdef CFG_OTHER
+#  error "per_config_c_debug built with CFG_OTHER"
+#endif
+void per_config_c_debug(void)
+{
+}