build/pkgs/sagelib/spkg-install: Do not poison SAGE_LOCAL, used in sc…

…ript installed by spkg pkgconf

build/pkgs/sagelib/spkg-install

@@ -4,8 +4,7 @@ cd "$SAGE_SRC"
 ## This is so that sagelib can be installed by standard Python procedures,
 ## such as "./setup.py install" or "pip install ."
 ##
-## We poison all environment variables that have paths to the sage source and build directories,
-## but keep the directories below SAGE_LOCAL intact.
+## We poison all environment variables that have paths to the sage source and build directories.
 ## In this way we make sure that all of the sagelib build's source paths are communicated through
 ## the current directory (for the source tree).
 ## Building takes places in the build/ subdirectory.
@@ -23,14 +22,20 @@ export SAGE_BUILD_DIR=/doesnotexist
 
 export PYTHON="$SAGE_LOCAL/bin/python3"
 
-export SAGE_LOCAL=/doesnotexist
+# We also poison all directories below SAGE_LOCAL.
+
 export SAGE_ETC=/doesnotexist
 export SAGE_PKGCONFIG=/doesnotexist
 export SAGE_PKG_CONFIG_PATH=/doesnotexist
 export SAGE_SPKG_SCRIPTS=/doesnotexist
 export SAGE_DOC=/doesnotexist
 export SAGE_SHARE=/doesnotexist
 
+# Trac #29411: We cannot poison SAGE_LOCAL because the pkg-config script
+# installed by the pkgconf spkg, generated from build/pkgs/pkgconf/patches/pkg-config.in,
+# uses this variable.
+# export SAGE_LOCAL=/doesnotexist
+
 time "$PYTHON" -u setup.py --no-user-cfg build install
 if [ "$UNAME" = "CYGWIN" ]; then
     sage-rebase.sh "$SAGE_LOCAL" 2>/dev/null;