Toolchain misc fixes

[th0ma7]

Description

Toolchain enhancements:

• Use status cookie to avoid regenerating tc_vars.*mk files
• Better handle logging messages
• Properly handle logging in the toolchain/syno-$(TC_NAME|ARCH)-$(TC_VERS) context
• Have spksrc.cross-cc.mk call toolchain generation instead of clunky spksrc.cross-env.mk
• Document each toolchain mk files
• Move all toolchain/syno-* no longer available to toolchain/archive
• Migrate DSM-6.2.4 to be using our github abandoned source URL
• Re-organize spksrc.toolchain/tc-version.mk to define per-DSM-version download URL
• Create a spksrc.toolchain/tc-base.mk and tc-url.mk to separate from compiler specific flags.
• Re-organize toolchain internal sub-mk files such as:

mk/spksrc.toolchain.mk
mk/spksrc.toolchain
├── tc-base.mk
├── tc-flags.mk
├── tc-normalize.mk
├── tc-rust.mk
├── tc-url.mk
├── tc_vars.mk
└── tc-versions.mk

Fixes

• Avoid multiple re-iteration of tc_var* toolchain generation
• Avoid generation of $(WORK_DIR)/tc_var* in dependencies folders
• Fix lgging at spk level that was missing

Other

• Enhanced significantly documentation of cross-cc|env.mk
• Create a $(call LOG_WRAPPED,<recipe>) default logging recipe

Checklist

• Build rule all-supported completed successfully
• New installation of package completed successfully
• Package upgrade completed successfully (Manually install the package again)
• Package functionality was tested
• Any needed documentation is updated/created

Type of change

• Bug fix
• New Package
• Package update
• Includes small framework changes
• This change requires a documentation update (e.g. Wiki)

[th0ma7]

@mreid-tt can you please test this PR? This is a major refactoring of the toolchain phase now using a two stage approach:
1- stage1 (bootstrap), install the toolchain and generate $(WORK_DIR)/tc_vars* configuration files (now only once)
2- stage2, cross-compile

This also now uses a generic LOG_WRAPPED macro so logging is uniquely managed throughout the build.

Really what's needed is testing builds and confirming all is still working as expected.

On my personnal TODO list: test kernel modules, certainly requires a small tweak.

EDIT: Tested against kernel packages and all is still running smoothly, no issue found.