5.1.1 Standard Symbols
All the generic macros that
AC_DEFINE a symbol as a result of
their test transform their argument values to a standard alphabet.
First, argument is converted to upper case and any asterisks
(‘*’) are each converted to ‘P’. Any remaining characters
that are not alphanumeric are converted to underscores.
defines the symbol ‘HAVE_STRUCT__EXPENSIVEP’ if the check