h5fortran not building with pruning enabled

[LKedward]

Copied from #676 (comment):

@LKedward , I found out, that fpm-0.6.0 doesn't compile correctly
geospace-code/h5fortran (it is compilable in fpm-0.5.0).

char_repeat_read                       failed.
[   5%]Compiling...
/usr/bin/ld: build/gfortran_ECCF645F41985A44/h5fortran/example_char_repeat_read.f90.o: in function `MAIN__':
h5fortran/example/char_repeat_read.f90:22: undefined reference to `__h5fortran_MOD_h5write_scalar'
/usr/bin/ld: h5fortran/example/char_repeat_read.f90:31: undefined reference to `__h5fortran_MOD_h5read_scalar'
/usr/bin/ld: build/gfortran_ECCF645F41985A44/h5fortran/libh5fortran.a(src_interface.f90.o):(.data.rel.ro+0x60): undefined reference to `__h5fortran_MOD_h5read_1d'
/usr/bin/ld: build/gfortran_ECCF645F41985A44/h5fortran/libh5fortran.a(src_interface.f90.o):(.data.rel.ro+0x70): undefined reference to `__h5fortran_MOD_h5read_3d'
/usr/bin/ld: build/gfortran_ECCF645F41985A44/h5fortran/libh5fortran.a(src_interface.f90.o):(.data.rel.ro+0x78): undefined reference to `__h5fortran_MOD_h5read_2d'
/usr/bin/ld: build/gfortran_ECCF645F41985A44/h5fortran/libh5fortran.a(src_interface.f90.o):(.data.rel.ro+0x88): undefined reference to `__h5fortran_MOD_h5read_4d'
/usr/bin/ld: build/gfortran_ECCF645F41985A44/h5fortran/libh5fortran.a(src_interface.f90.o):(.data.rel.ro+0x98): undefined reference to `__h5fortran_MOD_h5read_6d'
/usr/bin/ld: build/gfortran_ECCF645F41985A44/h5fortran/libh5fortran.a(src_interface.f90.o):(.data.rel.ro+0xa0): undefined reference to `__h5fortran_MOD_h5read_scalar'
/usr/bin/ld: build/gfortran_ECCF645F41985A44/h5fortran/libh5fortran.a(src_interface.f90.o):(.data.rel.ro+0xa8): undefined reference to `__h5fortran_MOD_h5write_1d'
/usr/bin/ld: build/gfortran_ECCF645F41985A44/h5fortran/libh5fortran.a(src_interface.f90.o):(.data.rel.ro+0xb0): undefined reference to `__h5fortran_MOD_h5write_3d'
/usr/bin/ld: build/gfortran_ECCF645F41985A44/h5fortran/libh5fortran.a(src_interface.f90.o):(.data.rel.ro+0xb8): undefined reference to `__h5fortran_MOD_h5write_4d'
/usr/bin/ld: build/gfortran_ECCF645F41985A44/h5fortran/libh5fortran.a(src_interface.f90.o):(.data.rel.ro+0xc0): undefined reference to `__h5fortran_MOD_h5write_2d'
/usr/bin/ld: build/gfortran_ECCF645F41985A44/h5fortran/libh5fortran.a(src_interface.f90.o):(.data.rel.ro+0xc8): undefined reference to `__h5fortran_MOD_h5read_7d'
/usr/bin/ld: build/gfortran_ECCF645F41985A44/h5fortran/libh5fortran.a(src_interface.f90.o):(.data.rel.ro+0xd0): undefined reference to `__h5fortran_MOD_h5read_5d'
/usr/bin/ld: build/gfortran_ECCF645F41985A44/h5fortran/libh5fortran.a(src_interface.f90.o):(.data.rel.ro+0xe0): undefined reference to `__h5fortran_MOD_h5write_6d'
/usr/bin/ld: build/gfortran_ECCF645F41985A44/h5fortran/libh5fortran.a(src_interface.f90.o):(.data.rel.ro+0xf0): undefined reference to `__h5fortran_MOD_h5write_scalar'
/usr/bin/ld: build/gfortran_ECCF645F41985A44/h5fortran/libh5fortran.a(src_interface.f90.o):(.data.rel.ro+0x168): undefined reference to `__h5fortran_MOD_h5write_7d'
/usr/bin/ld: build/gfortran_ECCF645F41985A44/h5fortran/libh5fortran.a(src_interface.f90.o):(.data.rel.ro+0x170): undefined reference to `__h5fortran_MOD_h5write_5d'
collect2: error: ld returned 1 exit status
<ERROR> Compilation failed for object " char_repeat_read "
<ERROR>stopping due to failed compilation
STOP 1

Taking h5write_scalar as an example, it seems that the submodule file is removed from the dependency tree.

ENV: Ubuntu, fpm-0.6.0 .

[LKedward]

Issue appears to be that grandchild submodules are being excluded from the build during pruning. I made an incorrect assumption in #676 that grandchild submodules only need to be built if their immediate parent is used elsewhere. Actually the whole submodule hierarchy needs to be built if the top-level parent is used.