Suppress a deprecation warning.

The solution for the warning in string.cpp will only arrive in C++26.

Author: gonsolo

CMakeLists.txt

@@ -660,6 +660,14 @@ SET (PBRT_UTIL_SOURCE
   src/pbrt/util/vecmath.cpp
 )
 
+# A warning about a deprecated function in C++17 but the solution will only be
+# in C++26.
+set_source_files_properties(
+    src/pbrt/util/string.cpp
+    PROPERTIES
+    COMPILE_FLAGS "-Wno-deprecated-declarations"
+)
+
 SET (PBRT_UTIL_SOURCE_HEADERS
   src/pbrt/util/args.h
   src/pbrt/util/bluenoise.h