Everytime I try to build Thunderbird ESR78 it stops with some compile errors for /ldap/c-sdk. System is macOS 10.15.

error: implicit declaration of function 'x' is invalid in C99 [-Werror,-Wimplicit-function-declaration]

I've tried so silence this by adding --disable-warnings-as-errors to my mozconfig, but this did not help. I've attached the full buildlog.

Thunderbird 77 did build without any error the same way.

This is not an issue for Firefox ESR78. Firefox ESR78 builds without any issue (same code, similar mozconifig).

Possibly you could get it building by adding -Wno-implicit-function-declaration

I guess the real fix is to properly include the right header files for that. I see

 2:55.03 /Volumes/Developer/mozilla-esr78/comm/ldap/c-sdk/libraries/liblber/io.c:162:12: error: implicit declaration of function 'read' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
 2:55.03       rc = read(sb->sb_sd, sb->sb_ber.ber_buf,
 2:55.03            ^
 2:55.03 /Volumes/Developer/mozilla-esr78/comm/ldap/c-sdk/libraries/liblber/io.c:162:12: note: did you mean 'fread'?
 2:55.03 /Volumes/Developer/Developer/SDKs/MacOSX10.15.sdk/usr/include/stdio.h:158:9: note: 'fread' declared here
 2:55.03 size_t   fread(void * __restrict __ptr, size_t __size, size_t __nitems, FILE * __restrict __stream);

(In reply to Magnus Melin [:mkmelin] from comment #2)

Possibly you could get it building by adding -Wno-implicit-function-declaration

Yes, this does work. Thanks. I thought --disable-warnings-as-errors is doing the same thing, but it seems not.

Looks like this was fixed in bug 1652906