[ROOT-9277] Unresolved symbol __emutls_v._ZSt11__once_call

[vepadulano]

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Description

From https://its.cern.ch/jira/browse/ROOT-9277

From https://root-forum.cern.ch/t/unresolved-symbols-when-using-std-async/28084/1 :

I am using root_v6.12.06.Linux-ubuntu17-x86_64-gcc7.2.tar.gz, the official binaries. I did want to speed up my code a lil bit with std::async and got such errors:

IncrementalExecutor::executeFunction: symbol '__emutls_v._ZSt11__once_call' unresolved while linking function '_GLOBAL__sub_I_cling_module_8'!
IncrementalExecutor::executeFunction: symbol '__emutls_v._ZSt15__once_callable' unresolved while linking function '_GLOBAL__sub_I_cling_module_8'!

Reproducer

std::async([]() { return 1; }).get();

ROOT version

Any

Installation method

Any

Operating system

Any

Additional context

Related to root-project/cling#370

[dpiparo]

still there with master.

[ferdymercury]

Also related: root-project/cling#321 root-project/cling#387

[dpiparo]

Still broken on linux but working on mac! :) @devajithvs ?