Implicit conversion from string_view to TString breaks existing code

lxplus780 ~ $ . /cvmfs/sft-nightlies.cern.ch/lcg/nightlies/dev3/Wed/ROOT/HEAD/x86_64-centos7-gcc9-opt/ROOT-env.sh 

lxplus780 ~ $ root -b

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  | (c) 1995-2019, The ROOT Team; conception: R. Brun, F. Rademakers |

  | Built for linuxx8664gcc on Jan 15 2020, 03:29:00                 |

  | From heads/master@v6-19-01-2427-g97e62a0                         |

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root [0] #include <TString.h>

root [1] std::string_view a = "a";

root [2] std::string b = "b";

root [3] a == b

ROOT_prompt_3:1:3: error: use of overloaded operator '==' is ambiguous (with operand types 'std::string_view' (aka 'basic_string_view<char>') and 'std::string' (aka 'basic_string<char>'))

a == b

~ ^  ~

/cvmfs/sft.cern.ch/lcg/releases/gcc/9.2.0-afc57/x86_64-centos7/bin/../lib/gcc/x86_64-pc-linux-gnu/9.2.0/../../../../include/c++/9.2.0/string_view:479:5: note: candidate function [with _CharT = char, _Traits = std::char_traits<char>]

    operator==(basic_string_view<_CharT, _Traits> __x,

    ^

/cvmfs/sft-nightlies.cern.ch/lcg/nightlies/dev3/Wed/ROOT/HEAD/x86_64-centos7-gcc9-opt/include/TEveUtil.h:99:6: note: candidate function

bool operator==(const TString& t, const std::string& s);

     ^

/cvmfs/sft-nightlies.cern.ch/lcg/nightlies/dev3/Wed/ROOT/HEAD/x86_64-centos7-gcc9-opt/include/TString.h:752:15: note: candidate function

inline Bool_t operator==(const TString &s1, const TString &s2)