build: Add compatibility with LLVM 20.1 (#1993)

This adds LLVM 20 compatibility. 
Fixes #1963.

Signed-off-by: Sven-Hendrik Haase <[email protected]>
Signed-off-by: Larry Gritz <[email protected]>
Co-authored-by: Larry Gritz <[email protected]>

Author: svenstaro

INSTALL.md

@@ -49,8 +49,8 @@ NEW or CHANGED minimum dependencies since the last major release are **bold**.
     $OpenImageIO_ROOT/lib to be in your LD_LIBRARY_PATH (or
     DYLD_LIBRARY_PATH on OS X).
 
-* [LLVM](http://www.llvm.org) 11, 12, 13, 14, 15, 16, 17, 18, or 19, including
-  clang libraries. **LLVM 20 is not yet supported.**
+* [LLVM](http://www.llvm.org) 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, including
+  clang libraries.
 
 * (optional) For GPU rendering on NVIDIA GPUs:
     * [OptiX](https://developer.nvidia.com/rtx/ray-tracing/optix) 7.0 or higher.

src/cmake/externalpackages.cmake

@@ -58,7 +58,7 @@ checked_find_package (pugixml REQUIRED
 # LLVM library setup
 checked_find_package (LLVM REQUIRED
                       VERSION_MIN 11.0
-                      VERSION_MAX 19.9
+                      VERSION_MAX 20.9
                       PRINT LLVM_SYSTEM_LIBRARIES CLANG_LIBRARIES
                             LLVM_SHARED_MODE)
 # ensure include directory is added (in case of non-standard locations

src/include/OSL/platform.h

@@ -20,6 +20,7 @@
 
 #include <cstring>
 #include <memory>
+#include <cstdint>
 
 #include <OSL/oslversion.h>