Fix missing module dependencies to 'xalloc'

[Bruno Haible]

A gnulib testdir for module 'xvasprintf' fails to build:

$ ./gnulib-tool --test --single-configure xvasprintf
...
../../gllib/xvasprintf.c: In function 'xstrcat':
../../gllib/xvasprintf.c:61:12: warning: implicit declaration of function 
'XNMALLOC' [-Wimplicit-function-declaration]
   result = XNMALLOC (totalsize + 1, char);
            ^
../../gllib/xvasprintf.c:61:37: error: expected expression before 'char'
   result = XNMALLOC (totalsize + 1, char);
                                     ^
make[4]: *** [Makefile:1541: xvasprintf.o] Error 1

The cause is the change
"xalloc-die: Fix link error with Solaris cc (regression 2020-07-27)"
from 2020-10-19. Module dependencies to 'xalloc' must now be explicitly
stated; a module dependency to 'xalloc-die' no longer implies one to 'xalloc'.

This patch fixes it; also in a couple of module for which the testdir
currently does not produce an error.


2020-11-22  Bruno Haible  <br...@clisp.org>

        Fix missing module dependencies to 'xalloc' (regression 2020-10-19).
        * modules/xvasprintf (Depends-on): Add xalloc.
        * modules/pipe-filter-gi (Depends-on): Likewise.
        * modules/execute (Depends-on): Likewise, for w32spawn.h.
        * modules/spawn-pipe (Depends-on): Likewise.

diff --git a/modules/execute b/modules/execute
index 857a188..a438fbf 100644
--- a/modules/execute
+++ b/modules/execute
@@ -29,6 +29,7 @@ stdlib
 strpbrk
 unistd
 environ
+xalloc
 
 configure.ac:
 gl_EXECUTE
diff --git a/modules/pipe-filter-gi b/modules/pipe-filter-gi
index 84e6cb3..152f909 100644
--- a/modules/pipe-filter-gi
+++ b/modules/pipe-filter-gi
@@ -19,6 +19,7 @@ stdint
 stdlib
 sys_select
 unistd
+xalloc
 
 configure.ac:
 AC_CHECK_FUNCS_ONCE([select])
diff --git a/modules/spawn-pipe b/modules/spawn-pipe
index ff19236..dd07fef 100644
--- a/modules/spawn-pipe
+++ b/modules/spawn-pipe
@@ -35,6 +35,7 @@ strpbrk
 unistd
 unistd-safer
 wait-process
+xalloc
 
 configure.ac:
 gl_SPAWN_PIPE
diff --git a/modules/xvasprintf b/modules/xvasprintf
index 410b45f..59d9a6e 100644
--- a/modules/xvasprintf
+++ b/modules/xvasprintf
@@ -14,6 +14,7 @@ m4/xvasprintf.m4
 
 Depends-on:
 vasprintf
+xalloc
 xalloc-die
 xsize
 stdarg