Trac #30657: Fix up "sage -p"

{{{
$ ./sage -p sagetex
Found local metadata for sagetex-3.5
Using cached file /Users/mkoeppe/s/sage/sage-
rebasing/upstream/sagetex-3.5.tar.gz
mkdir: : No such file or directory
************************************************************************
Error creating directory
************************************************************************
}}}

URL: https://trac.sagemath.org/30657
Reported by: mkoeppe
Ticket author(s): Matthias Koeppe
Reviewer(s): Michael Orlitzky

build/bin/sage-spkg

@@ -181,6 +181,9 @@ if [ -z "$SAGE_BUILD_DIR" ]; then
     export SAGE_BUILD_DIR="$SAGE_LOCAL/var/tmp/sage/build"
 fi
 
+export SAGE_SPKG_INST="$SAGE_LOCAL/var/lib/sage/installed"
+export SAGE_SPKG_SCRIPTS="$SAGE_LOCAL/var/lib/sage/scripts"
+export SAGE_SPKG_WHEELS="$SAGE_LOCAL/var/lib/sage/wheels"
 
 # Remove '.' from PYTHONPATH, to avoid trouble with setuptools / easy_install
 # (cf. #10192, #10176):

build/make/install

@@ -19,7 +19,10 @@ export SAGE_SHARE="$SAGE_LOCAL/share"
 export SAGE_PKGCONFIG="$SAGE_LOCAL/lib/pkgconfig"
 export SAGE_LOGS="$SAGE_ROOT/logs/pkgs"
 export SAGE_SPKG_INST="$SAGE_LOCAL/var/lib/sage/installed"
-export SAGE_SPKG_SCRIPTS="$SAGE_LOCAL/var/lib/sage/scripts"
+# Following line is duplicated here from build/bin/sage-spkg.
+# because the setting is also needed by some script packages.
+# The line here will be removed in #29386 (install script packages
+# via sage-spkg).
 export SAGE_SPKG_WHEELS="$SAGE_LOCAL/var/lib/sage/wheels"
 
 if [ -z "${SAGE_ORIG_PATH_SET}" ]; then