Ring3: Refactored out SysCallStackTop. #580

Job	Run time
Linux GCC	19m 38s
Linux GCC	19m 38s
Linux CLANGDWARF	21m 9s
Linux CLANGDWARF	21m 9s
Linux CLANGPDB	2m 24s
Linux CLANGPDB	21m 53s
macOS XCODE5	18m 58s
macOS XCODE5	18m 58s
Windows VS2019	29m 35s
Windows VS2019	29m 35s
Test	0s
Test (Ovmf, Ia32,X64,3264, XCODE5, RELEASE,DEBUG,NOOPT)	7m 58s
Test (Ovmf, Ia32,X64,3264, VS2019, RELEASE,DEBUG,NOOPT)	8m 19s
Test (Ovmf, Ia32,X64,3264, CLANGPDB, RELEASE,DEBUG,NOOPT)	8m 5s
Test (Ovmf, Ia32,X64,3264, CLANGDWARF, RELEASE,DEBUG,NOOPT)	8m 28s
Test (Ovmf, Ia32,X64,3264, GCC, RELEASE,DEBUG,NOOPT)	8m 0s
	4h 3m 47s

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