Use lhelper to manage the vendor libraries

[franko]

Simplifies the Makefile and remove the vendor directories to use instead lhelper to provides the external libraries.

I don't mean you should merge right away this PR except you really want to. I just would like to show you how my utility lhelper can be used to manage the external libraries, pcre2, lua and uthash.

The advantage it brings:

• simplified git clone (no recursive needed)
• smaller repositories without a vendor directory
• simplified Makefile that will automatically choose the libraries using pkg-config
• use an optimized build of each library with minimal options and static link by default
• can easily target any specific CPU architecture using the variables CPU_TYPE and CPU_TARGET
• easily create binary for official releases with minimal dependencies
• the same lhelper workflow works on Windows and macOS, the lhelper recipes are cross-platforms, built and tested on Windows and macOS too.

Lhelper will create an environment with the required libraries listed in the packages variable in build.lhelper. By default it will install the libraries for static linking and with minimal options.

There are two provided lhelper build files:

• build.lhelper will provide pcre2, lua 5.4 and uthash as static libraries
• build-system-deps.lhelper will provide only uthash and for pcre2 and lua the system provide dev packages will be used instead

To illustrate how minimal are the run-time dependencies of the executable, the binary I built using build.lhelper only needs the following dynamic libraries:

linux-vdso.so.1 (0x00007fffd05cd000) libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f7d889d1000) libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f7d889cb000) libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f7d887d9000) /lib64/ld-linux-x86-64.so.2 (0x00007f7d88c26000)

so it does depend only on the system provided libc which is a pretty good compromise to work on most linux distributions.