remove clang headers conflicting with FreeBSD headers

[alfredo]

Summary

Some clang headers are conflicting with FreeBSD headers. There was a previous patch that removed them from package install, but it was reverted on revision r459483 as it was believe that now works properly.
I identified that conflict still exists, during my tests cross compiling from x86_64 to powerpc64 host using llvm-devel package.

This change reintegrates the previous patch and include more files, matching the ones that are removed from src BASE:

in /usr/src/lib/clang/headers/Makefile :

Headers which possibly conflict with our own versions:
.if defined(INSTALL_CONFLICTING_CLANG_HEADERS)
INCS+=          float.h
INCS+=          intrin.h
INCS+=          inttypes.h
INCS+=          iso646.h
INCS+=          limits.h
INCS+=          stdalign.h
INCS+=          stdarg.h
INCS+=          stdatomic.h
INCS+=          stdbool.h
INCS+=          stddef.h
INCS+=          stdint.h
INCS+=          stdnoreturn.h
INCS+=          tgmath.h
INCS+=          unwind.h
INCS+=          varargs.h
.endif

Test Plan

build clang (from /usr/ports/devel/llvm-devel)
build src base using clang-devel (CC=clang-devel, CXX=clang++-devel and so)

[alfredo]

Error output example:

/usr/local/bin/clang-devel -target powerpc64-unknown-freebsd13.0 --sysroot=/usr/obj/usr/src/powerpc.powerpc64/tmp -B/usr/obj/usr/src/powerpc.powerpc64/tmp/usr/bin  -O2 -pipe   -DNO__SCCSID -DNO__RCSID -I/usr/src/lib/libc/include -I/usr/src/include -I/usr/src/lib/libc/powerpc64 -DNLS  -D__DBINTERFACE_PRIVATE -I/usr/src/contrib/gdtoa -I/usr/src/contrib/libc-vis -DINET6 -I/usr/obj/usr/src/powerpc.powerpc64/lib/libc -I/usr/src/lib/libc/resolv -D_ACL_PRIVATE -DPOSIX_MISTAKE -I/usr/src/lib/libmd -I/usr/src/contrib/jemalloc/include -I/usr/src/contrib/tzcode/stdtime -I/usr/src/lib/libc/stdtime -I/usr/src/lib/libc/locale -DBROKEN_DES -DPORTMAP -DDES_BUILTIN -I/usr/src/lib/libc/rpc -DYP -DNS_CACHING -DSYMBOL_VERSIONING -g -MD  -MF.depend.getgrent.o -MTgetgrent.o -std=gnu99 -fstack-protector-strong -Wsystem-headers -Werror -Wall -Wno-format-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/lib/libutil -I/usr/src/lib/msun/powerpc -I/usr/src/lib/msun/src -c /usr/src/lib/libc/gen/getgrent.c -o getgrent.o
In file included from /usr/src/lib/libc/gen/getgrent.c:55:
/usr/src/include/stdio.h:77:19: error: redefinition of typedef 'va_list' is a C11 feature [-Werror,-Wtypedef-redefinition]
typedef __va_list       va_list;
                        ^
/usr/local/llvm-devel/lib/clang/8.0.0/include/stdarg.h:30:27: note: previous definition is here
typedef __builtin_va_list va_list;
                          ^
1 error generated.
*** [getgrent.o] Error code 1

make[4]: stopped in /usr/src/lib/libc
1 error

[brooks]

What version of FreeBSD is your system running? I'm happy to commit this, but want to make sure I understand the issue fully.

[alfredo]

In D18879#403032, @brooks wrote:

What version of FreeBSD is your system running? I'm happy to commit this, but want to make sure I understand the issue fully.

I'm using two systems in my tests:
1 - x84_64 machine cross compiling base to powerpc64-elfv2 running: FreeBSD 12.0-RC3 FreeBSD 12.0-RC3 r341271 GENERIC amd64
2 - powerpc64 machine "cross" compiling base to powerpv64-elfv2 running: FreeBSD 12.0-RELEASE r341666 GENERIC

the conflicts are between libraries at /usr/obj/usr/src/powerpc.powerpc64/tmp/usr/include/ and the ones instaled by llvm-devel ports at /usr/local/llvm-devel/lib/clang/8.0.0/include/

[brooks]

I'll commit shortly