unstable twiss crashes madx about cpymad

[coldfix]

Debugging with gdb:

% gdb python
[...]

(gdb) run -c 'from cpymad.libmadx import start, input; start(); input("call, file=example.madx;")'
[...]
enter Twiss module
 TWDISP: Unable to compute intial dispersion --- dispersion set to zero.
 Singular matrix occurred during closed orbit search.
/home/thomas/.virtualenvs/madgui/bin/python: 
Thread 1 "python" received signal SIGSEGV, Segmentation fault.
0x00007ffff7f1a27c in __strchrnul_avx2 () from /usr/lib/libc.so.6

(gdb) bt
#0  0x00007ffff7f1a27c in __strchrnul_avx2 () from /usr/lib/libc.so.6
#1  0x00007ffff7e0b7fe in vfprintf () from /usr/lib/libc.so.6
#2  0x00007ffff7e0e666 in buffered_vfprintf () from /usr/lib/libc.so.6
#3  0x00007ffff7e0bc12 in vfprintf () from /usr/lib/libc.so.6
#4  0x00007ffff7eb3a6c in error_tail () from /usr/lib/libc.so.6
#5  0x00007ffff7eb3c01 in error () from /usr/lib/libc.so.6
#6  0x00007ffff177d724 in seterrorflag ()
   from /home/thomas/hit/dev/cpymad/cpymad/libmadx.cpython-37m-x86_64-linux-gnu.so
#7  0x00007ffff17c5cf8 in pro_twiss ()
   from /home/thomas/hit/dev/cpymad/cpymad/libmadx.cpython-37m-x86_64-linux-gnu.so
#8  0x00007ffff18413ed in exec_command ()
   from /home/thomas/hit/dev/cpymad/cpymad/libmadx.cpython-37m-x86_64-linux-gnu.so
#9  0x00007ffff177db95 in process ()
   from /home/thomas/hit/dev/cpymad/cpymad/libmadx.cpython-37m-x86_64-linux-gnu.so
#10 0x00007ffff177fe47 in pro_input_ ()
   from /home/thomas/hit/dev/cpymad/cpymad/libmadx.cpython-37m-x86_64-linux-gnu.so
#11 0x00007ffff177a0a0 in madx_input ()
   from /home/thomas/hit/dev/cpymad/cpymad/libmadx.cpython-37m-x86_64-linux-gnu.so
#12 0x00007ffff1841a66 in exec_command ()
   from /home/thomas/hit/dev/cpymad/cpymad/libmadx.cpython-37m-x86_64-linux-gnu.so
#13 0x00007ffff177db95 in process ()
   from /home/thomas/hit/dev/cpymad/cpymad/libmadx.cpython-37m-x86_64-linux-gnu.so
#14 0x00007ffff177fe47 in pro_input_ ()

[coldfix]

This occurs due to naming conflict: error resolves to error(3) from libc within the python process space (since libc is loaded earlier?)

[coldfix]

Patched in MethodicalAcceleratorDesign/MAD-X#678, should be included in 5.04.02. Can also be avoided by building MAD-X with -DCMAKE_C_FLAGS="-fvisibility=hidden".