A double pointer was being passed to the call to FortranStart rather than just a pointer to the EnvironmentDefaults.list. This now passes `null` directly when there's no EnvironmentDefaults.list and passes the list directly when there is, removing the original global variable which was a pointer to a pointer containing null or the EnvironmentDefaults.list global.
Fixes#90537
This patch changes the behaviour for flang to only create and link to a
`main` entry point when the Fortran code has a program statement in it.
This means that flang-new can be used to link even when the program is
a mixed C/Fortran code with `main` present in C and no entry point
present in Fortran.
This also removes the `-fno-fortran-main` flag as this no longer has any
functionality.
To accomplish this, this patch creates an optional list of environment
variable default values to be set by the runtime to allow directly using
the existing runtime implementation of FORT_CONVERT for I/O conversions.
