lib/55310: implicit conversion error when compiling current amd64 with clang

[rares.aioanei%gmail.com@localhost]

>Number:         55310
>Category:       lib
>Synopsis:       implicit conversion error when compiling current amd64 with clang
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    lib-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu May 28 07:55:00 +0000 2020
>Originator:     Rares Aioanei
>Release:        CURRENT
>Organization:
>Environment:
n/a
>Description:
This happens when cross-compiling on FreeBSD 12.1-RELEASE amd64 as well as on my NetBSD CURRENT amd64 box, using clang exactly as instructed in the docs, by altering mk.conf  : 

#   compile  libntp/timexsup.o                                                                                                                                                                
/stpool/devel/netbsd/current/amd64/usr/src/obj/tooldir.FreeBSD-12.1-RELEASE-p3-amd64/bin/x86_64--netbsd-clang -O2  -std=gnu99     -Wno-sign-compare -Wno-pointer-sign  -Wall -Wstrict-prototyp
es -Wmissing-prototypes -Wpointer-arith -Wno-sign-compare    -Wreturn-type -Wswitch -Wshadow -Wcast-qual -Wwrite-strings -Wextra -Wno-unused-parameter -Wno-sign-compare -Wsign-compare -Wform
at=2   -Wpointer-sign -Wmissing-noreturn  -Werror -Wno-missing-noreturn -Wno-unneeded-internal-declaration  -Wno-parentheses -Wno-constant-logical-operand  -Wno-error=unused-const-variable  
-fPIE    --sysroot=/stpool/devel/netbsd/current/amd64/usr/src/obj/destdir.amd64 -DHAVE_CONFIG_H -I/stpool/devel/netbsd/current/amd64/usr/src/external/bsd/ntp/include  -I/stpool/devel/netbsd/
current/amd64/usr/src/external/bsd/ntp/dist/include  -I/stpool/devel/netbsd/current/amd64/usr/src/external/bsd/ntp/dist/lib/isc/include  -I/stpool/devel/netbsd/current/amd64/usr/src/external
/bsd/ntp/dist/lib/isc/unix/include  -I/stpool/devel/netbsd/current/amd64/usr/src/external/bsd/ntp/dist/lib/isc/nothreads/include -DOPENSSL -DAUTOKEY -DUSE_OPENSSL_CRYPTO_RAND -DWANT_IPV6 -I/
stpool/devel/netbsd/current/amd64/usr/src/external/bsd/ntp/dist/sntp/libopts  -c    /stpool/devel/netbsd/current/amd64/usr/src/external/bsd/ntp/dist/libntp/timexsup.c -o timexsup.o
/stpool/devel/netbsd/current/amd64/usr/src/external/bsd/ntp/dist/libntp/timexsup.c:33:14: error: implicit conversion from 'long' to 'double' changes value from 9223372036854775807 to 9223372
036854775808 [-Werror,-Wimplicit-int-float-conversion]                                    
        if (dval >= LONG_MAX)                                                                  
                 ~~ ^~~~~~~~
/stpool/devel/netbsd/current/amd64/usr/src/obj/destdir.amd64/usr/include/machine/limits.h:56:18: note: expanded from macro 'LONG_MAX'
#define LONG_MAX        0x7fffffffffffffffL     /* max value for a long */
                        ^~~~~~~~~~~~~~~~~~~
1 error generated.
*** [timexsup.o] Error code 1

nbmake[10]: stopped in /stpool/devel/netbsd/current/amd64/usr/src/external/bsd/ntp/lib/libntp
1 error

>How-To-Repeat:
compile latest CURRENT amd64 with clang
>Fix:
n/a