lib/54050: malloc_usable_size() is provided on recent NetBSD-current, however malloc.h has no prototype

[ryoon%NetBSD.org@localhost]

>Number:         54050
>Category:       lib
>Synopsis:       malloc_usable_size() is provided on recent NetBSD-current, however malloc.h has no prototype
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    lib-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Mar 09 03:40:00 +0000 2019
>Originator:     Ryo ONODERA
>Release:        NetBSD 8.99.35
>Organization:
	
>Environment:
	
	
System: NetBSD brownie 8.99.35 NetBSD 8.99.35 (DTRACE7) #8: Sat Mar 9 02:41:18 JST 2019 ryoon@brownie:/usr/world/8.99/amd64/obj/sys/arch/amd64/compile/DTRACE7 amd64
Architecture: x86_64
Machine: amd64
>Description:
It seems that recent NetBSD-current with jemalloc provides
malloc_usable_size(), however /usr/include/malloc.h has
no prototype definition.

This inconsistency breaks a build of pkgsrc/www/firefox-65.0.2nb1.
	
>How-To-Repeat:
	
cd /usr/pkgsrc/www/firefox
make install
>Fix:
	
I will add a workaround for pkgsrc/www/firefox.
However modifying malloc.h is preferable, if malloc_usable_size()
works well.

>Unformatted: