Fix compilation with Clang++

[nsoranzo]

The 2 commits in this PR are required to build muscle for bioconda: https://github.com/bioconda/bioconda-recipes/pull/29550

Replace zero macro with memset_zero

The zero and memset_zero macros defined in myutils.h are the same, but zero interferes with LLVM's libcxx when compiling on macOS using Clang:

In file included from addconfseq.cpp:1:
In file included from ./muscle.h:23:
In file included from ./multisequence.h:4:
In file included from ./sequence.h:6:
In file included from /usr/local/miniconda/envs/bioconda/conda-bld/muscle_1644453677064/_build_env/bin/../include/c++/v1/fstream:184:
In file included from /usr/local/miniconda/envs/bioconda/conda-bld/muscle_1644453677064/_build_env/bin/../include/c++/v1/ostream:137:
In file included from /usr/local/miniconda/envs/bioconda/conda-bld/muscle_1644453677064/_build_env/bin/../include/c++/v1/ios:215:
In file included from /usr/local/miniconda/envs/bioconda/conda-bld/muscle_1644453677064/_build_env/bin/../include/c++/v1/__locale:18:
In file included from /usr/local/miniconda/envs/bioconda/conda-bld/muscle_1644453677064/_build_env/bin/../include/c++/v1/mutex:190:
/usr/local/miniconda/envs/bioconda/conda-bld/muscle_1644453677064/_build_env/bin/../include/c++/v1/__mutex_base:447:25: error: too few arguments provided to function-like macro invocation
    if (__d <= __d.zero())
                        ^
./myutils.h:361:9: note: macro 'zero' defined here
#define zero(a, n)      memset((a), 0, (n)*sizeof(a[0]))
        ^
1 error generated.
make: *** [Makefile:53: Darwin/addconfseq.o] Error 1

This is the call to zero in libcxx:

https://github.com/llvm/llvm-project/blob/b35be6fe98e30b2373e8fdf024ef8c13a32121d7/libcxx/include/__mutex_base#L444

which is supposed to call:

https://en.cppreference.com/w/cpp/chrono/duration/zero

Move va_start/va_end out of critical section

Fix the following error when compiling with Clang++:

myutils.cpp:912:2: error: 'va_start' cannot be used in a captured statement
        va_start(ArgList, Format);
        ^
1 error generated.
make: *** [Makefile:53: Darwin/myutils.o] Error 1

Solution inspired by: https://github.com/Ultimaker/CuraEngine/pull/1124

[nsoranzo]

muscle 5.1 conda package just released thanks to these patches: https://anaconda.org/bioconda/muscle

[rcedgar]

thanks @nsoranzo 👍