nss: Fix warnings generated by getcwd

getcwd() conforms to POSIX.1-2001 which leaves the behaviour when the
buf argument is NULL, undefined. This makes gcc 10+ throw the following
warning:

argument 1 is null but the corresponding size argument 2 value is 4096

Initially, this was fixed by disabling NSS_ENABLE_WERROR. This patch
re-enables NSS_ENABLE_WERROR (by leaving it to its default value) and
takes advantage of the existing functionality in nss that wraps the
getcwd call into a function making sure that the buf argument is always
properly allocated.

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-oe/recipes-support/nss/nss_3.60.1.bb

@@ -76,7 +76,6 @@ do_compile_prepend_class-native() {
 
 do_compile() {
     export NSPR_INCLUDE_DIR=${STAGING_INCDIR}/nspr
-    export NSS_ENABLE_WERROR=0
 
     export CROSS_COMPILE=1
     export NATIVE_CC="${BUILD_CC}"
@@ -84,6 +83,10 @@ do_compile() {
     export NATIVE_FLAGS="${BUILD_CFLAGS} -DLINUX -Dlinux"
     export BUILD_OPT=1
 
+    # POSIX.1-2001 states that the behaviour of getcwd() when passing a null
+    # pointer as the buf argument, is unspecified.
+    export NATIVE_FLAGS="${NATIVE_FLAGS} -DGETCWD_CANT_MALLOC"
+
     export FREEBL_NO_DEPEND=1
     export FREEBL_LOWHASH=1