libgdal.so exposes symbols from libshapefile

[pnicolas]

In our Linux application we use both gdal and ​shapelib, compiled as a shared library (.so).

Gdal internally uses shapelib as well and exposes the symbols. If we do not pay attention to the order of parameters in the linking phase, functions like SHPOpen will link to libgdal.so instead of libshp.so.

This can be solved by adding -fvisibility=hidden to CPPFLAGS in ogr/ogrsf_frmts/shape/GNUmakefile

without fsivility flag: global symbol

nm gdal.so | grep 'SHPOpen$'
0000000000bb82af T SHPOpen

with fsivility flag: local symbol

nm gdal.so | grep 'SHPOpen$'
0000000000bb3cd3 t SHPOpen

[Even Rouault]

In 37996:

Shape: do not export Shapelib symbols for builds --with-hide-internal-symbols (fixes #6860)

[Even Rouault]

In 37997:

Shape: do not export Shapelib symbols for builds --with-hide-internal-symbols (fixes #6860)