guix: consolidate glibc 2.27 package

Refactor our glibc 2.27 to be a single 'package', and avoid the use of
`package-with-extra-configure-variable`. This also lets us drop the
`enable_werror` workaround, and just use --disable-werror directly.

Employ the same workaround as the Guix glibc, to avoid a "permission
denied" failure during build:
```bash
make  subdir=sunrpc -C sunrpc ..=../ subdir_install
make[2]: Entering directory '/tmp/guix-build-glibc-cross-x86_64-linux-gnu-2.27.drv-0/source/sunrpc'
.././scripts/mkinstalldirs /gnu/store/ga8jciqrd5lh52m572x3mk4q1smf5agq-glibc-cross-x86_64-linux-gnu-2.27/include/rpc
mkdir -p -- /gnu/store/ga8jciqrd5lh52m572x3mk4q1smf5agq-glibc-cross-x86_64-linux-gnu-2.27/include/rpc
/gnu/store/kvpvk5wh70wdbjnr83hh85rg22ysxm9h-coreutils-8.32/bin/install -c -m 644 rpc/netdb.h /gnu/store/ga8jciqrd5lh52m572x3mk4q1smf5agq-glibc-cross-x86_64-linux-gnu-2.27/include/rpc/netdb.h
.././scripts/mkinstalldirs /gnu/store/ga8jciqrd5lh52m572x3mk4q1smf5agq-glibc-cross-x86_64-linux-gnu-2.27/include/nfs
mkdir -p -- /gnu/store/ga8jciqrd5lh52m572x3mk4q1smf5agq-glibc-cross-x86_64-linux-gnu-2.27/include/nfs
/gnu/store/kvpvk5wh70wdbjnr83hh85rg22ysxm9h-coreutils-8.32/bin/install -c -m 644 ../sysdeps/unix/sysv/linux/nfs/nfs.h /gnu/store/ga8jciqrd5lh52m572x3mk4q1smf5agq-glibc-cross-x86_64-linux-gnu-2.27/include/nfs/nfs.h
/gnu/store/kvpvk5wh70wdbjnr83hh85rg22ysxm9h-coreutils-8.32/bin/install -c -m 644 /tmp/guix-build-glibc-cross-x86_64-linux-gnu-2.27.drv-0/build/gnu/lib-names-64.h /gnu/store/ga8jciqrd5lh52m572x3mk4q1smf5agq-glibc-cross-x86_64-linux-gnu-2.27/include/gnu/lib-names-64.h
/gnu/store/kvpvk5wh70wdbjnr83hh85rg22ysxm9h-coreutils-8.32/bin/install -c -m 644 etc.rpc /etc/rpc
/gnu/store/kvpvk5wh70wdbjnr83hh85rg22ysxm9h-coreutils-8.32/bin/install: cannot create regular file '/etc/rpc': Permission denied
make[2]: *** [Makefile:197: /etc/rpc] Error 1
```

contrib/guix/manifest.scm

@@ -83,11 +83,11 @@ FILE-NAME found in ./patches relative to the current file."
                                         xbinutils))
          ;; 3. Build a cross-compiled libc with XGCC-SANS-LIBC and XKERNEL,
          ;; derived from BASE-LIBC
-         (xlibc (explicit-cross-configure (cross-libc target
+         (xlibc (cross-libc target
-                                                      base-libc
+                            base-libc
-                                                      xgcc-sans-libc
+                            xgcc-sans-libc
-                                                      xbinutils
+                            xbinutils
-                                                      xkernel)))
+                            xkernel))
          ;; 4. Build a cross-compiling gcc targeting XLIBC, derived from
          ;; BASE-GCC
          (xgcc (explicit-cross-configure (cross-gcc target
@@ -130,7 +130,7 @@ chain for " target " development."))
                                        #:key
                                        (base-gcc-for-libc base-gcc)
                                        (base-kernel-headers base-linux-kernel-headers)
-                                       (base-libc (hardened-glibc glibc-2.27))
+                                       (base-libc glibc-2.27)
                                        (base-gcc (make-gcc-rpath-link (hardened-gcc base-gcc))))
   "Convenience wrapper around MAKE-CROSS-TOOLCHAIN with default values
 desirable for building Bitcoin Core release binaries."
@@ -513,17 +513,6 @@ and endian independent.")
 inspecting signatures in Mach-O binaries.")
       (license license:expat))))
 
-;; https://www.gnu.org/software/libc/manual/html_node/Configuring-and-compiling.html
-;; We don't use --disable-werror directly, as that would be passed through to bash,
-;; and cause it's build to fail.
-(define (hardened-glibc glibc)
-  (package-with-extra-configure-variable (
-    package-with-extra-configure-variable (
-      package-with-extra-configure-variable glibc
-      "enable_werror" "no")
-      "--enable-stack-protector" "all")
-      "--enable-bind-now" "yes"))
-
 (define-public mingw-w64-base-gcc
   (package
     (inherit base-gcc)
@@ -556,7 +545,28 @@ inspecting signatures in Mach-O binaries.")
               (patches (search-our-patches "glibc-2.27-riscv64-Use-__has_include-to-include-asm-syscalls.h.patch"
                                            "glibc-2.27-fcommon.patch"
                                            "glibc-2.27-guix-prefix.patch"
-                                           "glibc-2.27-no-librt.patch"))))))
+                                           "glibc-2.27-no-librt.patch"))))
+    (arguments
+      (substitute-keyword-arguments (package-arguments glibc)
+        ((#:configure-flags flags)
+          `(append ,flags
+            ;; https://www.gnu.org/software/libc/manual/html_node/Configuring-and-compiling.html
+            (list "--enable-stack-protector=all",
+                  "--enable-bind-now",
+                  "--disable-werror",
+                  building-on)))
+    ((#:phases phases)
+        `(modify-phases ,phases
+           (add-before 'configure 'set-etc-rpc-installation-directory
+             (lambda* (#:key outputs #:allow-other-keys)
+               ;; Install the rpc data base file under `$out/etc/rpc'.
+               ;; Otherwise build will fail with "Permission denied."
+               (let ((out (assoc-ref outputs "out")))
+                 (substitute* "sunrpc/Makefile"
+                   (("^\\$\\(inst_sysconfdir\\)/rpc(.*)$" _ suffix)
+                    (string-append out "/etc/rpc" suffix "\n"))
+                   (("^install-others =.*$")
+                    (string-append "install-others = " out "/etc/rpc\n"))))))))))))
 
 (packages->manifest
  (append