Fix duplicate symbol cpp2::Uncaught_exceptions()

[filipsajdak]

5575ec4 added new symbols to cpp2util.h that caused the linker to find a duplicate symbol of cpp2::Uncaught_exceptions().

Linking multiple cpp2 files ends with:

[build] duplicate symbol 'cpp2::Uncaught_exceptions()' in:
[build]     libs/execspec/CMakeFiles/libexecspec.dir/src/application.cpp.o
[build]     libs/markdown/CMakeFiles/libmarkdown.dir/src/markdown.cpp.o
[build] duplicate symbol 'cpp2::Uncaught_exceptions()' in:
[build]     libs/execspec/CMakeFiles/libexecspec.dir/src/application.cpp.o
[build]     libs/execspec/CMakeFiles/libexecspec.dir/src/compile_cpp2.cpp.o
[build] duplicate symbol 'cpp2::Uncaught_exceptions()' in:
[build]     libs/execspec/CMakeFiles/libexecspec.dir/src/application.cpp.o
[build]     apps/execspec/CMakeFiles/execspec.dir/src/main.cpp.o
[build] ld: 3 duplicate symbols for architecture arm64

This change adds inline to cpp2::Uncaught_exceptions() function that fixes an error.

[hsutter]

Thanks!