feat: option for strict flag usage (#1430)

When compiling yaml-cpp as a root project flags like -Wall -pedantic or
-pedantic-error are being set. Some compilers report false positives
and/or are not aware of certain flags.
While having a strict compile policy is nice but hinders people who are
using rare compiler or compiler configurations or sometimes just new
compiler.

The current workaround is to edit the CMakeLists.txt file and edit out
those flags.

This patch provides a new CMake option "YAML_CPP_USE_STRICT_FLAGS".
The default value is set to ON if its the
root project, otherwise OFF. This allows a user to call `cmake
-DYAML_CPP_USE_STRICT_FLAGS=OFF .." to deactivate any strict flag
settings.

log: feat: option for strict flag usage

Author: SGSSGene

CMakeLists.txt

@@ -21,6 +21,7 @@ option(YAML_CPP_FORMAT_SOURCE "Format source" ${YAML_CPP_MAIN_PROJECT})
 option(YAML_CPP_DISABLE_UNINSTALL  "Disable uninstallation of yaml-cpp" OFF)
 option(YAML_USE_SYSTEM_GTEST "Use system googletest if found" OFF)
 option(YAML_ENABLE_PIC "Use Position-Independent Code " ON)
+option(YAML_CPP_USE_STRICT_FLAGS "Uses strict compilation flags e.g.: -Wall" ${YAML_CPP_MAIN_PROJECT})
 
 cmake_dependent_option(YAML_CPP_BUILD_TESTS
   "Enable yaml-cpp tests" OFF
@@ -92,7 +93,7 @@ if (NOT DEFINED CMAKE_CXX_STANDARD)
       CXX_STANDARD 11)
 endif()
 
-if(YAML_CPP_MAIN_PROJECT)
+if (YAML_CPP_USE_STRICT_FLAGS)
   target_compile_options(yaml-cpp
     PRIVATE
       $<${print-warnings}:-Wall -Wextra -Wshadow -Weffc++ -Wno-long-long>