Revert "temp: fail build on gcc 6"

This reverts commit 574cd279

.travis.yml

@@ -58,20 +58,6 @@ matrix:
           packages:
             - g++-8
 
-      # ARM g++ 6 on Linux with C++14
-    - env: COMPILER=g++-6 BUILD=Debug STANDARD=14
-      compiler: gcc
-      arch: arm64
-      os: linux
-      dist: xenial
-      addons:
-        apt:
-          update: true
-          sources:
-            - ubuntu-toolchain-r-test
-          packages:
-            - g++-6
-
       # Apple clang on OS X with C++14
     - env: BUILD=Debug STANDARD=14
       compiler: clang

test/CMakeLists.txt

@@ -83,9 +83,6 @@ function(add_fmt_test name)
   if (FMT_WERROR)
     target_compile_options(${name} PRIVATE ${WERROR_FLAG})
   endif ()
-  if (CMAKE_CXX_COMPILER_ID MATCHES "GNU")
-    target_compile_options(${name} PRIVATE -fvisibility=hidden -Werror=attributes)
-  endif()
   target_include_directories(${name} SYSTEM PUBLIC gtest gmock)
   add_test(NAME ${name} COMMAND ${name})
 endfunction()