Created attachment 226650 [details]
electron12 poudriere log of build failiure on amd64 stable 13
The port devel/electron12 fails to build on amd64 stable 13 using poudriere with the following error:
static declaration of 'mempcpy' follows non-static declaration
static inline void *mempcpy(void *dst, const void *src, size_t n)
/usr/include/string.h:70:7: note: previous declaration is here
void *mempcpy(void * __restrict, const void * __restrict, size_t);
Just want to add this is related to the same error occurring for the Chromium build bug where mempcpy was added to base libc as shown below:
Created attachment 227006 [details]
Patch based on Bug257352 for www/chromium
Does this patch work for you?
I myself cannot try due to dependency conflicts. (node, yarn,...)
This is based on patch for Bug 257352. 
Makefile part is modified to fit devel/electron12.
(And date and time of original files.)
Thanks. Will give this patch a try and report back on how it goes.
Electron seems to have built successfully here with this patch applied.
Thanks for the fix.
Created attachment 227998 [details]
Patch based on Bug257352 and Bug258271 for www/chromium
Avoid warning on previous patch while building Index for branches not yet MFC'ed mempcpy() addition.
Actually, merge previous patch and proposed fix for www/chromium on Bug258271, v2 patch by Felix.
So the patch fixed the build problem stated in the ticket, but curious if anyone got this further down the line:
../../sandbox/linux/suid/sandbox.c:12:10: fatal error: 'asm/unistd.h' file not found
(In reply to Daniel Shafer from comment #6)
As I wrote on past comment, I myself cannot build-test devel/electron12 due to dependency conflict. would need some other person to look in and fix. Sorry.
*I remember that initial devel/electron* port was derived from www/chromium and
found this PR, so ported the fix for www/chromium by hand.
But I "feel" it seems to be a lack of dependency.
For my case, /compat/linux/usr/include/asm/unistd.h was installed by package linux-c7-devtools-7.9.2009 and www/chromium builds fine at git 9e6695a71d64.
*Build after commit git 17218fbbe799 is on-going just now.
(In reply to Tomoaki AOKI from comment #7)
So I added it as a dependency just to see, and it still wouldn't build. Not sure much about this, if there is anything I can test I will be happy to do so.