feat: Adding SPDX identifiers to source/build files #478

Job	Run time
Windows MSVC x64	1m 28s
Windows MSVC x86	1m 50s
Windows MSVC ARM64	1m 43s
Windows GCC	2m 8s
Windows Clang	1m 28s
Ubuntu GCC	33s
Ubuntu Clang	32s
MUSL Cross Compile x86_64	1m 11s
MUSL Cross Compile i686	45s
MUSL Cross Compile aarch64	57s
MUSL Cross Compile armv7l	53s
MUSL Cross Compile armv6	52s
MUSL Cross Compile armv5l	48s
MUSL Cross Compile powerpc64	55s
MUSL Cross Compile powerpc64le	1m 0s
provenance	0s
	17m 3s

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