MFC r314101: don't use C99 static array indices with older GCC versions

Sponsored by: Panzura

MFC r314100: fix a typo in __STDC_VERSION__ in __min_size requirements

MFC r307584 (partially)

307584 added the __min_size macro and replaced some static array sizes with
__min_size. However, stable/10 doesn't yet have any static array sizes, so
all this MFC does is add the __min_size macro.

Original commit message:

Fix C++ includability of crypto headers with static array sizes

C99 allows array function parameters to use the static keyword for their
sizes. This tells the compiler that the parameter will have at least the
specified size, and calling code will fail to compile if that guarantee is
not met. However, this syntax is not legal in C++.

This commit reverts r300824, which worked around the problem for
sys/sys/md5.h only, and introduces a new macro: min_size(). min_size(x) can
be used in headers as a static array size, but will still compile in C++
mode.

MFC r300967:

Stop exposing the C11 _Atomic() macro in <sys/cdefs.h>, when compiling
for C++. It clashes with the one in libc++'s <atomic> header.

(Previously, the _Atomic() macro was defined in <stdatomic.h>, which is
only for use with C11, but for various reasons it was moved to its
current location in r251804.)

Discussed with: bdrewery, ed

MFC r284858:

Enable the use of __builtin_va_* for ICC.

PR: 198822
Submitted by: Sergey Melnikov <sergey.melnikov@intel.com>

MFC r284743:
Rename __weak to __weak_symbol to avoid language conflict with objective-C.

PR: 200972 (exp-run)
Suggested by: theraven@

MFC r268137, r268138:

Define a "__weak" macro for declaring symbols "weak".

Add support for empty data sets. Data set begin and end pointers
should resolve to "NULL" when not present. This is done by declaring
the data set begin and end symbols as "weak".

MFC r282863:

Adjust visibility macros.

The GCC visibility attributes were introduced in GCC 4.0.
Apparently the "protected" attribute was introduced only
until GCC 4.2, but we are not currently using it.

Revert r280449;
Permit multiple arguments for the nonnull attribute.

For the benefit of anyone that may be struggling to port
FreeBSD to gcc 2.8 (or older) avoid using variadic macros.

MFC r280700 (partial);

Bring new attribute:
__result_use_check
Causes a warning to be emitted if a caller of the function
with this attribute does not use its return value. This is
known in gcc as "warn_unused_result" but we considered the
original naming unsuitable for an attribute.

MFC r280273;
Permit multiple arguments for the nonnull attribute.

This is very useful for non-trivial functions and doesn't
affect existing uses.

MFC r278222:

Mark typedefs for manually implementing _Static_assert() as unused, so
they won't show up unecessarily for -Wunused-local-typedefs.

MFC r277883:

Ensure that lint does not pick up C11 keywords (e.g. _Noreturn), even
if C11 mode is used. It does not support any C11 constructs.

MFC r284858:

Enable the use of __builtin_va_* for ICC.

PR: 198822
Submitted by: Sergey Melnikov <sergey.melnikov@intel.com>

MFC r284743:
Rename __weak to __weak_symbol to avoid language conflict with objective-C.

PR: 200972 (exp-run)
Suggested by: theraven@

MFC r268137, r268138:

Define a "__weak" macro for declaring symbols "weak".

Add support for empty data sets. Data set begin and end pointers
should resolve to "NULL" when not present. This is done by declaring
the data set begin and end symbols as "weak".

MFC r282863:

Adjust visibility macros.

The GCC visibility attributes were introduced in GCC 4.0.
Apparently the "protected" attribute was introduced only
until GCC 4.2, but we are not currently using it.

Revert r280449;
Permit multiple arguments for the nonnull attribute.

For the benefit of anyone that may be struggling to port
FreeBSD to gcc 2.8 (or older) avoid using variadic macros.

MFC r280700 (partial);

Bring new attribute:
__result_use_check
Causes a warning to be emitted if a caller of the function
with this attribute does not use its return value. This is
known in gcc as "warn_unused_result" but we considered the
original naming unsuitable for an attribute.

MFC r280273;
Permit multiple arguments for the nonnull attribute.

This is very useful for non-trivial functions and doesn't
affect existing uses.

MFC r278222:

Mark typedefs for manually implementing _Static_assert() as unused, so
they won't show up unecessarily for -Wunused-local-typedefs.

MFC r277883:

Ensure that lint does not pick up C11 keywords (e.g. _Noreturn), even
if C11 mode is used. It does not support any C11 constructs.