String_val returns const char*

[MisterDA]

No description provided.

[rjbou]

ping @dra27

[MisterDA]

This is required in order to build Opam with OCaml 4.10. I think that discarding the const qualifier is a warning by default, but it’s been turned into an error when compiling Opam.

[MisterDA]

The errors this PR fixes are:

Command [288] exited with code 2:
$ (cd _build/default/src/stubs && C:\cygwin64\opt\OCamlPlatform\bin\ocamlc.opt.exe -g -ccopt -nologo -ccopt -O2 -ccopt -Gy- -ccopt -MD -ccopt /WX -o opamWindows.obj opamWindows.c)
opamWindows.c(386): error C2220: the following warning is treated as an error
opamWindows.c(386): warning C4090: '=': different 'const' qualifiers
opamWindows.c(572): warning C4090: 'function': different 'const' qualifiers
opamWindows.c(573): warning C4090: 'function': different 'const' qualifiers
opamWindows.c(741): warning C4090: 'function': different 'const' qualifiers
opamWindows.c(741): warning C4090: 'function': different 'const' qualifiers

[dra27]

Sorry for the delay reviewing. There's a load of legacy #ifdef _WIN32 which are unnecessary (and incorrect) and these stubs should be upgraded to support Unicode properly, but the changes here are completely correct, thanks!