ENABLE_JS_SYSTRACE_TO_ETW (JS ETW Tracing) is Unintentionally Always Disabled

[NickGerleman]

In #3934 we introduced a subtle build-logic issue which leads to ENABLE_JS_SYSTRACE_TO_ETW always being disabled. We had intended to only enable it when using patched React Native, but end up comparing against a literal string instead of a property. See '$PATCH_RN'=='true' in the following condition.

<PreprocessorDefinitions Condition="'$(ENABLE_JS_SYSTRACE_TO_ETW)'=='true' AND '$PATCH_RN'=='true'">ENABLE_JS_SYSTRACE_TO_ETW;WITH_FBSYSTRACE;%(PreprocessorDefinitions)</PreprocessorDefinitions>

Reenabling this on deforked React Native leads to build errors:

d:\react-native-windows\vnext\reactwindowscore\tracing\fbsystrace.h(71): error C2664: 'void fbsystrace::FbSystraceSection::init(void)': cannot convert argument 1 from 'const double' to 'std::string &&' (compiling source file D:\react-native-windows\vnext\build\x64\Debug\ReactCommon\react-native-patched\ReactCommon\jsiexecutor\jsireact\JSIExecutor.cpp)
2>  d:\react-native-windows\vnext\reactwindowscore\tracing\fbsystrace.h(69): note: Reason: cannot convert from 'const double' to 'std::string' (compiling source file D:\react-native-windows\vnext\build\x64\Debug\ReactCommon\react-native-patched\ReactCommon\jsiexecutor\jsireact\JSIExecutor.cpp)
2>  d:\react-native-windows\vnext\reactwindowscore\tracing\fbsystrace.h(69): note: No constructor could take the source type, or constructor overload resolution was ambiguous (compiling source file D:\react-native-windows\vnext\build\x64\Debug\ReactCommon\react-native-patched\ReactCommon\jsiexecutor\jsireact\JSIExecutor.cpp)
2>  d:\react-native-windows\vnext\reactwindowscore\tracing\fbsystrace.h(82): note: see reference to function template instantiation 'void fbsystrace::FbSystraceSection::init<const double&>(std::string &&,const double &)' being compiled (compiling source file D:\react-native-windows\vnext\build\x64\Debug\ReactCommon\react-native-patched\ReactCommon\jsiexecutor\jsireact\JSIExecutor.cpp)
2>  d:\react-native-windows\vnext\build\x64\debug\reactcommon\react-native-patched\reactcommon\cxxreact\systracesection.h(30): note: see reference to function template instantiation 'fbsystrace::FbSystraceSection::FbSystraceSection<const char(&)[11],const double&>(uint64_t,std::string &&,const char (&)[11],const double &)' being compiled (compiling source file D:\react-native-windows\vnext\build\x64\Debug\ReactCommon\react-native-patched\ReactCommon\jsiexecutor\jsireact\JSIExecutor.cpp)
2>  d:\react-native-windows\vnext\build\x64\debug\reactcommon\react-native-patched\reactcommon\jsiexecutor\jsireact\jsiexecutor.cpp(233): note: see reference to function template instantiation 'facebook::react::ConcreteSystraceSection::ConcreteSystraceSection<const char(&)[11],const double&>(const char *,const char (&)[11],const double &)' being compiled
2>  d:\react-native-windows\node_modules\.folly\folly-2019.09.30.00\folly\range.h(1356): note: see reference to class template instantiation 'folly::Range<const char *>' being compiled (compiling source file D:\react-native-windows\vnext\build\x64\Debug\ReactCommon\react-native-patched\ReactCommon\jsiexecutor\jsireact\JSIExecutor.cpp)

We can fix this without much issue in 0.60-stable, but need to think a bit harder in how to do it in 0.61 where we don't use the fork.

[NickGerleman]

@mganandraj what do you think the impact of this is? How urgent do you think it is to backport a fix to 0.60-stable?