Merge linux-crosscompile, improve build script, add CI build and release pipelines

[NoMore201]

PR introduces following changes:

• Merge linux-crosscompile branch to allow cross-compilation of Windows toolchain from linux
• Make build script use parametric CFLAGS, CXXFLAGS and LDFLAGS. If not set from environment,
  script will use default values
• Refactor build script to have a cleaner command line interface
• Various shellcheck fixes and properly format file using only spaces
• all now compiles both windows and linux toolchains. Added a new linux build steps to build only linux toolchain

[NoMore201]

UPDATE: last commit e40c62deaafec864cbf99f745a4342b25c756878 adds github actions pipeline that builds compiler artifact for both Windows and Linux on each push.
Moreover, when a new Release is published through github releases, it will publish build artifacts from the pipeline that has run for that specific commit/tag. You can have a look to the outcome of this in my fork: https://github.com/NoMore201/tricore-gcc-toolchain/releases/tag/v11.3.1-cb09676

[NoMore201]

Last commit 0efb81c introduces a fix for Win32 build that caused lib/gcc/tricore-elf/11.3.1/libgcc.a to be compiled with dwarf version 5 symbols, which made ELF file not recognizable by some debuggers (like PLS Universal Debug Engine that seems to only support dwarf v3 symbols)

[NoMore201]

Abandoning this PR, since I'm working on a new solution involving GNU autoconf/automake. A new PR will follow shortly.