meson: Propagate optimization flag for linking on Emscripten

Emscripten uses the optimization flag at link time to enable optimizations
via Binaryen [1]. While meson.build currently recognizes the -Doptimization
option, it does not propagate it to the linking. This commit updates
meson.build to propagate the optimization flag to the linking when targeting
WebAssembly.

[1] https://emscripten.org/docs/optimizing/Optimizing-Code.html#how-emscripten-optimizes

Signed-off-by: Kohei Tokunaga <[email protected]>

Author: ktock

meson.build

@@ -869,6 +869,10 @@ elif host_os == 'openbsd'
     # Disable OpenBSD W^X if available
     emulator_link_args = cc.get_supported_link_arguments('-Wl,-z,wxneeded')
   endif
+elif host_os == 'emscripten'
+  if get_option('optimization') != 'plain'
+    emulator_link_args += ['-O' + get_option('optimization')]
+  endif
 endif
 
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