build: support building all tools in a single binary

Add the --enable-single-binary option to the configure file.
When enabled, this option builds a single binary file containing
the selected tools.  Which tool gets executed depends on the value
of argv[0] which can be set implicitly through symlinks to the
single program.

This setup reduces significantly the size of a complete coreutils
install, since code from lib/libcoreutils.a is not duplicated in
every one of the more than 100 binaries.  Runtime overhead is
increased due to more dynamic libraries being loaded, and extra
initialization being performed for all utils.  Also initially
a larger binary is loaded from storage, though this is usually
alleviated due to caching and lazy mmaping of unused blocks,
and in fact the single binary should have better caching
characteristics.

Comparing the size of the individual versus single binary on x86_64:
  $ cd src
  $ size coreutils
  $ size -t $(../build-aux/gen-lists-of-programs.sh --list-progs |
              grep -Ev '(coreutils|libstdbuf)') | tail -n1
     text    data     bss     dec     hex filename
  1097416    5388   88432 1191236  122d44 src/coreutils
  4901010  124964  163768 5189742  4f306e (TOTALS)

Storage requirements are reduced similarly:
  $ cd src
  $ du -h coreutils
  $ du -ch $(../build-aux/gen-lists-of-programs.sh --list-progs |
             grep -Ev '(coreutils|libstdbuf)') | tail -n1
  1.2M    coreutils
  5.3M    total

When installing, the makefile will create either symlinks or
shebangs based on the --enable-single-binary setting, for
each configured tool. In this way, all the tools are still
callable individually, but they are all implemented by the same
"coreutils" binary installed on the same directory.

* .gitignore: Add new generated files.
* Makefile.am: New rules to generate build-aux/gen-single-binary.sh
  and install symlinks.
* NEWS: Mention the new feature.
* README: Add "coreutils" to the list of utils.
* bootstrap.conf: Regenerate src/single-binary.mk
* build-aux/gen-lists-of-programs.sh: New --list-progs option.
* build-aux/gen-single-binary.sh: Regenerate
* configure.ac: New --enable-single-binary option and other variables.
Disallow --enable-single-binary=symlinks with --program-prefix et. al.
* man/coreutils.x: Manpage hook.
* man/local.mk: Add manpage hook and fix dependencies.
* src/coreutils.c: Multicall implementation.
* src/local.mk: New rules for the single binary option.
* tests/local.mk: Add $single_binary_progs to support
require_built_() from init.cfg
* tests/misc/env.sh: Avoid the use of symlink to echo.
* tests/misc/help-version.sh: Add exception for coreutils.
* tests/install/basic-1.sh: Really avoid using ginstall strip
functionality if there is an issue with the independent strip command.
* src/kill.c: Changes to call exit() in main.
* src/readlink.c: Likewise.
* src/shuf.c: Likewise.
* src/timeout.c: Likewise.
* src/truncate.c: Likewise.

1 files changed, 19 insertions, 0 deletions

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 96220c350..19a523d8e 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -47,6 +47,7 @@
 * chroot: (coreutils)chroot invocation.         Specify the root directory.
 * cksum: (coreutils)cksum invocation.           Print POSIX CRC checksum.
 * comm: (coreutils)comm invocation.             Compare sorted files by line.
+* coreutils: (coreutils)coreutils invocation.   Multi-call program.
 * cp: (coreutils)cp invocation.                 Copy files.
 * csplit: (coreutils)csplit invocation.         Split by context.
 * cut: (coreutils)cut invocation.               Print selected parts of lines.
@@ -229,6 +230,7 @@ Common Options
 * Traversing symlinks::          Traversing symlinks to directories
 * Treating / specially::         Treating / specially
 * Standards conformance::        Standards conformance
+* coreutils invocation::         Multi-call binary invocation
 
 Output of entire files
 
@@ -771,6 +773,7 @@ name.
 * Treating / specially::        --preserve-root and --no-preserve-root.
 * Special built-in utilities::  @command{break}, @command{:}, @dots{}
 * Standards conformance::       Conformance to the POSIX standard.
+* coreutils invocation::        Multi-call binary invocation.
 @end menu
 
 
@@ -1494,6 +1497,22 @@ that assumes an older version of POSIX and uses @samp{sort +1}
 or @samp{tail +10}, you can work around any compatibility problems by setting
 @samp{_POSIX2_VERSION=199209} in your environment.
 
+@node coreutils invocation
+@section @command{coreutils}: Multi-call binary
+
+@pindex multicall
+@cindex combined
+@cindex calling combined multi-call binary
+
+@command{coreutils} invokes an individual utility, either
+implicitly selected by the last component of @samp{argv[0]},
+or by explicitly calling @command{coreutils} with the
+@option{--coreutils-prog} option.  Synopsis:
+
+@example
+coreutils @option{--coreutils-prog=PROGRAM} @dots{}
+@end example
+
 @node Output of entire files
 @chapter Output of entire files