gnu: nss: Prepare for GCC 10.

* gnu/packages/patches/nss-getcwd-nonnull.patch: New file.
* gnu/local.mk (dist_patch_DATA): Adjust accordingly.
* gnu/packages/nss.scm (nss)[source](patches): Add it.

gnu/local.mk

@@ -1439,6 +1439,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/network-manager-plugin-path.patch	\
   %D%/packages/patches/nginx-socket-cloexec.patch		\
   %D%/packages/patches/nsis-env-passthru.patch			\
+  %D%/packages/patches/nss-getcwd-nonnull.patch			\
   %D%/packages/patches/nss-increase-test-timeout.patch		\
   %D%/packages/patches/nss-3.56-pkgconfig.patch			\
   %D%/packages/patches/ntfs-3g-CVE-2019-9755.patch		\

gnu/packages/nss.scm

@@ -96,6 +96,7 @@ (define-public nss
                 (file-name (git-file-name name version))
                 ;; Create nss.pc and nss-config.
                 (patches (search-patches "nss-3.56-pkgconfig.patch"
+                                         "nss-getcwd-nonnull.patch"
                                          "nss-increase-test-timeout.patch"))
                 (modules '((guix build utils)))
                 (snippet

gnu/packages/patches/nss-getcwd-nonnull.patch

@@ -0,0 +1,30 @@
+Disable -Werror=nonnull on getcwd(0, 4096) because GCC incorrectly warns that
+the second argument should be NULL with recent glibc.  See:
+
+https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96832
+https://sourceware.org/bugzilla/show_bug.cgi?id=26545
+
+diff --git a/coreconf/nsinstall/nsinstall.c b/coreconf/nsinstall/nsinstall.c
+--- a/coreconf/nsinstall/nsinstall.c
++++ b/coreconf/nsinstall/nsinstall.c
+@@ -236,14 +236,20 @@ main(int argc, char **argv)
+ 	return 0;
+ 
+     if (!cwd) {
++#pragma GCC diagnostic push
++#pragma GCC diagnostic ignored "-Wnonnull"
+ 	cwd = GETCWD(0, PATH_MAX);
++#pragma GCC diagnostic pop
+ 	if (!cwd)
+ 	    fail("could not get CWD");
+     }
+ 
+     /* make sure we can get into todir. */
+     xchdir(todir);
++#pragma GCC diagnostic push
++#pragma GCC diagnostic ignored "-Wnonnull"
+     todir = GETCWD(0, PATH_MAX);
++#pragma GCC diagnostic pop
+     if (!todir)
+ 	fail("could not get CWD in todir");
+     tdlen = strlen(todir);