compiling with ports llvm11 breaks on mman.h: struct shm_larg epage_conf

Hi,

Because I'm tired of hours of compilation of llvm/clang I'm testing  
compiling FreeBSD with llvm11 from a pkg.

Setup a jail with 13-CURRENT. Compilation of the installed version went  
fine.
Today I svn up'd and compiled and compilation broke.

/lib/clang/11.0.0/include -fstack-protector-strong -Wsystem-headers  
-Werror -Wall -[29/1822]
t-y2k -Wno-uninitialized -Wno-pointer-sign -Wno-empty-body  
-Wno-string-plus-int -Wno-unused-const-variable -Wno-tautological-compare  
-Wno-unused-value -Wno-parentheses-equality -Wno-unused-function  
-Wno-enum-conversion -Wno-unused-local-typedef  
-Wno-address-of-packed-member -
Wno-switch -Wno-switch-enum -Wno-knr-promoted-parameter   
-Qunused-arguments    -I/usr/src/li
b/libutil -I/usr/src/lib/msun/amd64 -I/usr/src/lib/msun/x86  
-I/usr/src/lib/msun/src -c /usr/
src/lib/libc/sys/shm_open.c -o shm_open.o
/usr/src/lib/libc/sys/shm_open.c:64:28: error: variable has incomplete  
type 'struct shm_larg
epage_conf'
         struct shm_largepage_conf slc;
                                   ^
/usr/src/lib/libc/sys/shm_open.c:64:9: note: forward declaration of  
'struct shm_largepage_co
nf'
         struct shm_largepage_conf slc;


I can see the difference between /usr/include/sys/mman.h and  
/usr/src/sys/sys/mman.h is exactly about these symbols.
Why is the base compiler using the latter and ports llvm11 the former?

Configuration of my src.conf and make.conf is described in  
https://blog.klop.ws/2020/08/waiting-for-clang-forever-and-ever.html .


Do I miss some directive about system header files?

Regards,

Ronald.