Some compilation fixes

[Horst H. von Brand]

On Fedora 34 the following fixes are needed to build nuweb. Compiling with CFLAGS='-g -O2 -Wall' reports some unused variables, I deleted most of them. Attached git patches against frob (8267eaf), renamed to .txt to appease github.

A troubling warning I can't fix offhand is:

scraps.c: In function ‘search’:
scraps.c:1316:28: warning: array subscript 1025 is above array bounds of ‘char[1024]’ [-Warray-bounds]
 1316 |          c = m->prev->chars[SLAB_SIZE - k];
      |              ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
scraps.c:6:8: note: while referencing ‘chars’
    6 |   char chars[SLAB_SIZE];
      |        ^~~~~

This comes from the piece (at line 6082):

@d Get the nth previous character from a scrap
@{int k = m->index - n - 2;

if (k >= 0)
   c = m->scrap->chars[k];
else if (m->prev)
   c = m->prev->chars[SLAB_SIZE - k];
@}

It is seen that k should be 0 here, and the chars member is defined of size SLAB_SIZE, so this gives an out of bounds access.

There are some further warnings that I'll dig into later. Perhaps also try latest clang and crank up warnings...

0001-Fix-link-errors-warnings.patch.txt
0002-Propagate-fixes-to-generated-files.patch.txt
0003-Add-nuweb-nuweb-to-.gitignore.patch.txt