[Web] Fix build failure on Windows

[AThousandShips]

Follow up to:

• [Web] Use actual PThread pool size for get_default_thread_pool_size() #104458

In PowerShell (at least, haven't tried with other shells) the pipe characters are not interpreted as part of the expression, leading to:

[ 67%] em++: error: error parsing "-s" setting "PTHREAD_POOL_SIZE='Module[emscriptenPoolSize]": unclosed quoted string. expected final character to be "'" and length to be greater than 1 in "'"
[ 68%] '8'' is not recognized as an internal or external command, operable program or batch file.

Swapping the quote characters solves this issue (though I don't know how to confirm that the result is parsed correctly in either case)

[akien-mga]

I can't test easily, but given that CI passed it seems to not impact the build from Linux.

Could you confirm this works on Windows in both PowerShell and cmd.exe?

[AThousandShips]

Can confirm that:

• The original bug also occurs in cmd
• This fixes the same bug with cmd and it builds correctly

[Repiteo]

Thanks!

[AThousandShips]

Thank you!