Using thread-local storage may not be desired in all environments
and/or use-cases, thus there should be an option to disable its use
on purpose.

Fixes #451.

This is intended to provide a way, during development, to test out the memory
and performance impacts of a change.

On Windows, or at least when cross-built with Mingw-w64, build fails
because strict prototype fails on an included file (thus nothing we can
do about in json-c code):

> from /home/jehan/dev/src/json-c/json_util.c:44:
> /home/jehan/.local/share/crossroad/roads/w64/json-c/include/minwindef.h:196:3: error: function declaration isn't a prototype [-Werror=strict-prototypes]
>   196 |   typedef INT_PTR (WINAPI *FARPROC) ();
>       |   ^~~~~~~
> /home/jehan/.local/share/crossroad/roads/w64/json-c/include/minwindef.h:197:3: error: function declaration isn't a prototype [-Werror=strict-prototypes]
>   197 |   typedef INT_PTR (WINAPI *NEARPROC) ();
>       |   ^~~~~~~
> /home/jehan/.local/share/crossroad/roads/w64/json-c/include/minwindef.h:198:3: error: function declaration isn't a prototype [-Werror=strict-prototypes]
>   198 |   typedef INT_PTR (WINAPI *PROC) ();
>       |   ^~~~~~~

Let's just disable the errors for Windows build.

The default location for pkconfig files on most systems is:
  ${CMAKE_INSTALL_LIBDIR}/pkgconfig

Thus the file should get installed in there by default.

Linking with '-Bsymbolic-functions' is supported for ELF-binaries, only.

There was a typo in `CMAKE_SHARED_LINKER_FLAGS`.

Add uninstall target in cmake

modify json-c default build type, and fix up the assert() errors in t…

add uint64 data to json-c

Include all compiler warnings, and provide DISABLE_WERROR to make them not be errors.
 Define _REENTRANT, if setting it works.
 Set -Bsymbolic-functions, and provide DISABLE_BSYMBOLIC to turn that off.
 Implement the check for HAS_GNU_WARNING_LONG

CMake was not properly substituting the installation dir variables (they
ended up all empty), so the pkg-config results were also wrongs. For
instance cflags was: -I -I/json-c
Even though json-c was found at configure time, this obviously broke the
build of any application using it.

Now json-c can be bundled to any cmake-based project and used with
couple lines of code:

add_subdirectory(json-c EXCLUDE_FROM_ALL)
target_link_libraries(MyProject json-c)