gnu: Add a "debug" output for some packages.

* gnu/packages/base.scm (coreutils, gnu-make, glibc): Add a "debug" output.
* gnu/packages/bdw-gc.scm (libgc): Likewise.
* gnu/packages/guile.scm (guile-2.0): Likewise.
* gnu/packages/libffi.scm (libffi): Likewise.
* gnu/packages/multiprecision.scm (gmp, mpfr, mpc): Likewise.

gnu/packages/base.scm

@@ -279,6 +279,7 @@ The tools supplied with this package are:
              ,@(if (%current-target-system)
                    '()
                    `(("perl" ,perl)))))
+   (outputs '("out" "debug"))
    (arguments
     `(#:parallel-build? #f            ; help2man may be called too early
       #:phases (alist-cons-before
@@ -316,6 +317,7 @@ are expected to exist on every operating system.")
    (build-system gnu-build-system)
    (native-inputs
     `(("patch/impure-dirs" ,(search-patch "make-impure-dirs.patch"))))
+   (outputs '("out" "debug"))
    (arguments
     '(#:patches (list (assoc-ref %build-inputs "patch/impure-dirs"))
       #:phases (alist-cons-before
@@ -403,7 +405,7 @@ BFD (Binary File Descriptor) library, `gprof', `nm', `strip', etc.")
    ;; reference to them anyway, so there's no space savings here.
    ;; TODO: Eventually we may want to add a $LOCALE_ARCHIVE search path like
    ;; Nixpkgs does.
-   (outputs '("out" "locales"))
+   (outputs '("out" "locales" "debug"))
 
    (arguments
     `(#:out-of-source? #t

gnu/packages/bdw-gc.scm

@@ -39,6 +39,7 @@
     ;; Make it so that we don't rely on /proc.  This is especially useful in
     ;; an initrd run before /proc is mounted.
     '(#:configure-flags '("CPPFLAGS=-DUSE_LIBC_PRIVATES")))
+   (outputs '("out" "debug"))
    (synopsis "The Boehm-Demers-Weiser conservative garbage collector
 for C and C++")
    (description

gnu/packages/guile.scm

@@ -138,6 +138,8 @@ extensible.  It supports many SRFIs.")
 
    (self-native-input? #t)
 
+   (outputs '("out" "debug"))
+
    (arguments
     `(#:phases (alist-cons-before
                 'configure 'pre-configure

gnu/packages/libffi.scm

@@ -53,6 +53,7 @@
                  #:phases (alist-cons-after 'install 'post-install
                                             ,post-install-phase
                                             %standard-phases)))
+    (outputs '("out" "debug"))
     (synopsis "Foreign function call interface library")
     (description
      "The libffi library provides a portable, high level programming interface

gnu/packages/multiprecision.scm

@@ -38,6 +38,7 @@
               "1hnbxz7a6jrli8ph27i8zb6k2f456zn6l5xi78yhskzbxjk47nf7"))))
    (build-system gnu-build-system)
    (native-inputs `(("m4" ,m4)))
+   (outputs '("out" "debug"))
    (arguments `(#:configure-flags
                 '(;; Build a "fat binary", with routines for several
                   ;; sub-architectures.
@@ -78,6 +79,7 @@ faster algorithms.")
             (sha256 (base32
                      "0fs501qi8l523gs3cpy4jjcnvwxggyfbklcys80wq236xx3hz79r"))))
    (build-system gnu-build-system)
+   (outputs '("out" "debug"))
    (propagated-inputs `(("gmp" ,gmp)))            ; <mpfr.h> refers to <gmp.h>
    (synopsis "C library for arbitrary precision floating-point arithmetic")
    (description
@@ -103,6 +105,7 @@ double-precision floating-point arithmetic (53-bit mantissa).")
             (sha256 (base32
                      "1zq0fidp1jii2j5k5n9hmx55a6wwid33gjzhimvxq9d5zrf82npd"))))
    (build-system gnu-build-system)
+   (outputs '("out" "debug"))
    (propagated-inputs `(("gmp" ,gmp)              ; <mpc.h> refers to both
                         ("mpfr" ,mpfr)))
    (synopsis "C library for arbitrary precision complex arithmetic")