Build errors with libtooling-based generator

[DemiMarie]

[1/13] Generating interface
FAILED: contrib/libxslt/libxslt_sapi.sapi.h /home/user/sandboxed-api/build/contrib/libxslt/libxslt_sapi.sapi.h 
cd /home/user/sandboxed-api/build/contrib/libxslt && /home/user/sandboxed-api/build/sandboxed_api/tools/clang_generator/sapi_generator_tool -p /home/user/sandboxed-api/build/contrib/libxslt --sapi_name=LibXSLT --sapi_out=libxslt_sapi.sapi.h --sapi_embed_dir=/home/user/sandboxed-api/build/contrib/libxslt --sapi_embed_name=libxslt_sapi --sapi_functions=xmlInitParser,sapi_xsltParseStylesheetDoc,xmlReadFd,xsltApplyStylesheet,xsltSaveResultToFile,xsltFreeStylesheet,xmlFreeDoc,xmlSaveToFd,xmlSaveDoc,xmlSaveFlush,xmlSaveClose --sapi_ns=sapi::contrib::libxslt /home/user/sandboxed-api/contrib/libxslt/wrapper.h
In file included from /home/user/sandboxed-api/contrib/libxslt/wrapper.h:4:
In file included from /usr/include/libxml2/libxml/SAX.h:15:
/usr/include/stdio.h:33:10: fatal error: 'stddef.h' file not found
#include <stddef.h>
         ^~~~~~~~~~
1 error generated.
Error while processing /home/user/sandboxed-api/contrib/libxslt/wrapper.h.
header generation failed

It looks like libtooling isn’t finding stddef.h, which is under /usr/lib/gcc/x86_64-redhat-linux/11/include on my system.