Tools,fsxc: nit, use longer flag for -c #1522

Job	Run time
linux-oldLTS-github--dotnet-and-xbuild	7m 21s
linux-oldLTS-github--dotnet-and-msbuild	7m 10s
macOS--dotnet6-and-mono	10m 40s
macOS--mono	10m 17s
linux-newLTS-github--dotnet-and-msbuild	8m 30s
linux-newLTS-github--dotnet-and-xbuild	8m 27s
linux-oldLTS-vanilla--stockmono	6m 56s
linux-oldLTS-vanilla--newmono	7m 53s
linux-newLTS-vanilla--dotnet6	7m 45s
linux-newLTS-vanilla--newmono	7m 0s
linux-newLTS-vanilla--stockmono	5m 13s
windows--legacyFramework	15m 6s
windows--dotnet6	8m 15s
sanity-check	1m 10s
publish	1m 17s
	1h 53m 0s

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