[feature] Support linear assembly of TI DSP

[Freed-Wu]

Same as cmake:

https://discourse.cmake.org/t/how-to-compile-linear-assemble/8122

$ cl6x --help
...
Default File Extensions Options:
  --ap_extension,-el=.ext      Extension for linear asm files (default is .sa)
  --asm_extension,-ea=.ext     Extension for assembly files (default is .asm)
  --c_extension,-ec=.ext       Extension for C files (default is .c)
...

TI DSP C compiler support linear assemble, which will not be detected by meson.

[Freed-Wu]

I suggest to add a new language name asm_linear like nasm, masm to solve this problem.