calc 2.12.6.9 release

The following are the changes in this release:

Fixed a number of core dump bugs related to the calculation of
tan(), cot(), sec(), csc(), tanh(), coth(), sech(), and csch(),
asin(), acos(), asinh(), acosh(), where when a call to an
underlying function produced an invalid value.  Thanks goes to
github user wuxiuheng for reporting this problem.

A number of trigonometric and hyperbolic functions that incorrectly
returned E_LOGINF, now return a new error code that is more
specific to the trigonometric or hyperbolic function.  The
following is a list of these new error codes: E_TAN3 E_TAN4
E_COT3 E_COT4 E_SEC3 E_CSC3 E_TANH3 E_TANH4 E_COTH3 E_COTH4
E_SECH3 E_CSCH3 E_ASIN3 E_ACOS3 E_ASINH3 E_ACOSH3 E_ATAN3 E_ACOT3
E_ASEC3 E_ACSC3 E_ATANH3 E_ACOTH3 E_ASECH3 E_ACSCH3.

Added regression tests 3729 thru 3732 to test E_TAN3, E_COT3,
E_SEC3 and E_CSC3 respectively.

Added experimential %g printf (and strprintf) format implementation
based on pull request from github user 10110111.

Made exterimental changes to macOS builds to not require use of
/usr/include.  The INCDIR for macOS uses:

INCDIR= $(shell xcrun --show-sdk-path --sdk macosx)/usr/include

to determine the upper path of the /usr/include directory for macOS.
The Darwin target seems to not automatically detected.  For now,
under macOS, declare the target as darwin:

# for macOS users only, force the target to be darwin
#
make target=Darwin clobber
make target=Darwin all
make target=Darwin chk
make target=Darwin install