gcc-wrapper: make __DATE__/__TIME__ deterministic

...when NIX_ENFORCE_PURITY=1.

@vcunat corrected the date according to docs.
https://gcc.gnu.org/onlinedocs/cpp/Standard-Predefined-Macros.html
In order to handle the spaces well, the extraAfter array had to be
quoted more properly and appended by +=.

pkgs/build-support/gcc-wrapper/gcc-wrapper.sh

@@ -84,11 +84,20 @@ fi
 extraAfter=($NIX_CFLAGS_COMPILE)
 extraBefore=()
 
+# When enforcing purity, pretend gcc can't find the current date and
+# time
+if test "$NIX_ENFORCE_PURITY" = "1"; then
+    extraAfter+=('-D__DATE__=??? ?? ????'
+        '-D__TIME__=??:??:??'
+        -Wno-builtin-macro-redefined)
+fi
+
+
 if test "$dontLink" != "1"; then
 
     # Add the flags that should only be passed to the compiler when
     # linking.
-    extraAfter=(${extraAfter[@]} $NIX_CFLAGS_LINK)
+    extraAfter+=($NIX_CFLAGS_LINK)
 
     # Add the flags that should be passed to the linker (and prevent
     # `ld-wrapper' from adding NIX_LDFLAGS again).
@@ -97,9 +106,9 @@ if test "$dontLink" != "1"; then
     done
     for i in $NIX_LDFLAGS; do
 	if test "${i:0:3}" = "-L/"; then
-	    extraAfter=(${extraAfter[@]} "$i")
+	    extraAfter+=("$i")
 	else
-	    extraAfter=(${extraAfter[@]} "-Wl,$i")
+	    extraAfter+=("-Wl,$i")
 	fi
     done
     export NIX_LDFLAGS_SET=1
@@ -139,9 +148,9 @@ fi
 # `-B' flags, since they confuse some programs.  Deep bash magic to
 # apply grep to stderr (by swapping stdin/stderr twice).
 if test -z "$NIX_GCC_NEEDS_GREP"; then
-    @gccProg@ ${extraBefore[@]} "${params[@]}" ${extraAfter[@]}
+    @gccProg@ ${extraBefore[@]} "${params[@]}" "${extraAfter[@]}"
 else
-    (@gccProg@ ${extraBefore[@]} "${params[@]}" ${extraAfter[@]} 3>&2 2>&1 1>&3- \
+    (@gccProg@ ${extraBefore[@]} "${params[@]}" "${extraAfter[@]}" 3>&2 2>&1 1>&3- \
         | (grep -v 'file path prefix' || true); exit ${PIPESTATUS[0]}) 3>&2 2>&1 1>&3-
     exit $?
 fi