Merge bitcoin/bitcoin#26994: depends: define __BSD_VISIBLE for FreeBSD bdb build

0e02f72 depends: define `__BSD_VISIBLE` for FreeBSD bdb build (fanquake)

Pull request description:

  Required for additional definitions (`IPC_R` & friends), to be available, when compiling under C11, which would otherwise cause compile fails.

  See: maflcko/bitcoin-core-nightly#4.

ACKs for top commit:
  hebasto:
    ACK 0e02f72, tested on FreeBSD 13.1:

Tree-SHA512: 885d4aa341d9668da360cf6dfafb97ce816803c54e76c0a06e448db39a723666d42cd14b3e713d17ecbe33163f5af69924567cf449d679a2db95b36357005d43

Author: merge-script

depends/packages/bdb.mk

@@ -15,7 +15,7 @@ $(package)_config_opts_netbsd=--with-pic
 $(package)_config_opts_openbsd=--with-pic
 $(package)_config_opts_android=--with-pic
 $(package)_cflags+=-Wno-error=implicit-function-declaration -Wno-error=format-security
-$(package)_cppflags_freebsd=-D_XOPEN_SOURCE=600
+$(package)_cppflags_freebsd=-D_XOPEN_SOURCE=600 -D__BSD_VISIBLE=1
 $(package)_cppflags_netbsd=-D_XOPEN_SOURCE=600
 $(package)_cppflags_openbsd=-D_XOPEN_SOURCE=600
 $(package)_cppflags_mingw32=-DUNICODE -D_UNICODE