All the cgo CPPFLAGS and CFLAGS directives in a package are concatenated and used to compile C files in that package. All the CPPFLAGS and CXXFLAGS directives in a package are concatenated and used to compile C++ files in that package. All the CPPFLAGS and FFLAGS directives in a package are concatenated and used to compile Fortran files in that package. All the LDFLAGS directives in any package in the program are concatenated and used at link time. All the pkg-config directives are concatenated and sent to pkg-config simultaneously to add to each appropriate set of command-line flags.
On Windows:
set CGO_CXXFLAGS=-std=c++11