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On macOS Sierra (OSX 10.12.1):
 $ ./configure --with-pydebug && make
 [... lots of output omitted ...]
 gcc -c -Wno-unused-result -Wsign-compare -g -O0 -Wall -Wstrict-prototypes -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -I. -I./Include -DPy_BUILD_CORE -o Python/random.o Python/random.c
 Python/random.c:97:19: warning: implicit declaration of function 'getentropy' is
 invalid in C99 [-Wimplicit-function-declaration]
 res = getentropy(buffer, len);
 ^
 1 warning generated.
This is because OSX 10.12.1 has getentropy() but does not have
getrandom(). You can see this in pyconfig.h:
 /* Define to 1 if you have the `getentropy' function. */
 #define HAVE_GETENTROPY 1
 /* Define to 1 if the getrandom() function is available */
 /* #undef HAVE_GETRANDOM */
and this means that in Python/random.c the header <sys/random.h> is
not included:
 # ifdef HAVE_GETRANDOM
 # include <sys/random.h>
 # elif defined(HAVE_GETRANDOM_SYSCALL)
 # include <sys/syscall.h>
 # endif
It's necessary include <sys/random.h> if either HAVE_GETRANDOM or
HAVE_GETENTROPY is defined.

New changeset 828251c2bccf by Ned Deily in branch '2.7':
Issue #28676: Prevent missing 'getentropy' declaration warning on macOS.
https://hg.python.org/cpython/rev/828251c2bccf
New changeset 0efd48d4c47c by Ned Deily in branch '3.5':
Issue #28676: Prevent missing 'getentropy' declaration warning on macOS.
https://hg.python.org/cpython/rev/0efd48d4c47c
New changeset e2faa8a22b69 by Ned Deily in branch '3.6':
Issue #28676: merge from 3.5
https://hg.python.org/cpython/rev/e2faa8a22b69
New changeset b31a7efd8b31 by Ned Deily in branch 'default':
Issue #28676: merge from 3.6
https://hg.python.org/cpython/rev/b31a7efd8b31 

Thanks for the patch, Gareth! Pushed for release in 2.7.13, 3.5.3, 3.6.0b4, and 3.7.0.