CPU family support 'sw_64' and remove the compile warning (#12273)

add sw_64 to the list of known cpus

docs/markdown/Reference-tables.md

@@ -128,11 +128,13 @@ set in the cross file.
 | sh4                 | SuperH SH-4              |
 | sparc               | 32 bit SPARC             |
 | sparc64             | SPARC v9 processor       |
+| sw_64               | 64 bit sunway processor  |
 | wasm32              | 32 bit Webassembly       |
 | wasm64              | 64 bit Webassembly       |
 | x86                 | 32 bit x86 processor     |
 | x86_64              | 64 bit x86 processor     |
 
+
 Any cpu family not listed in the above list is not guaranteed to
 remain stable in future releases.
 

mesonbuild/envconfig.py

@@ -68,6 +68,7 @@ known_cpu_families = (
     'sh4',
     'sparc',
     'sparc64',
+    'sw_64',
     'wasm32',
     'wasm64',
     'x86',
@@ -86,6 +87,7 @@ CPU_FAMILIES_64_BIT = [
     'riscv64',
     's390x',
     'sparc64',
+    'sw_64',
     'wasm64',
     'x86_64',
 ]