Trac #29793: script packages should cd into the SPKG directory

This simplifies several `spkg-install` scripts and make script packages
a bit more similar to normal packages.

This is a step towards #29386 (Install script packages via `sage-spkg`).

URL: https://trac.sagemath.org/29793
Reported by: mkoeppe
Ticket author(s): Matthias Koeppe
Reviewer(s): Michael Orlitzky

build/make/Makefile.in

@@ -574,15 +574,15 @@ endif
 #     $(3): package dependencies
 define SCRIPT_PACKAGE_templ
 $$(INST)/$(1)-$(2): $(3)
-	$(AM_V_at)cd '$$(SAGE_ROOT)' && \
+	$(AM_V_at)cd '$$(SAGE_ROOT)/build/pkgs/$(1)' && \
 		. '$$(SAGE_ROOT)/src/bin/sage-env' && . '$$(SAGE_ROOT)/build/bin/sage-build-env-config' && \
 		sage-logger -p '$$(SAGE_ROOT)/build/pkgs/$(1)/spkg-install' '$$(SAGE_LOGS)/$(1).log'
 	touch "$$@"
 
 $(1): $$(INST)/$(1)-$(2)
 
 $(1)-clean:
-	-$(AM_V_at)cd '$$(SAGE_ROOT)' && \
+	-$(AM_V_at)cd '$$(SAGE_ROOT)/build/pkgs/$(1)' && \
 		. '$$(SAGE_ROOT)/src/bin/sage-env' && . '$$(SAGE_ROOT)/build/bin/sage-build-env-config' && \
 		'$$(SAGE_ROOT)/build/pkgs/$(1)/spkg-uninstall'
 	-rm -f "$$(INST)/$(1)-$(2)"

build/pkgs/sage_conf/spkg-install

@@ -9,4 +9,4 @@ if [ $? -ne 0 ]; then
     echo >&2 "Is $SAGE_ROOT the correct SAGE_ROOT?"
     exit 1
 fi
-cd $SAGE_ROOT/build/pkgs/sage_conf/src && sdh_pip_install .
+cd src && sdh_pip_install .

build/pkgs/texlive/spkg-install

@@ -1 +1 @@
-exec sage-python23 build/pkgs/texlive/spkg-install.py
+exec sage-python23 spkg-install.py

src/doc/en/developer/packaging.rst

@@ -307,8 +307,9 @@ A script package has a single install script named ``spkg-install``.
 It needs to be an executable shell script; it is not subject to the templating
 described in the previous section.
 
-Sage runs ``spkg-install`` from the ``$SAGE_ROOT`` directory in the environment
-obtained by sourcing the files ``src/bin/sage-env`` and ``build/bin/sage-build-env-config``.
+Sage runs ``spkg-install`` from the directory ``$SAGE_ROOT/build/pkgs/<package>``
+in the environment obtained by sourcing the files ``src/bin/sage-env`` and
+``build/bin/sage-build-env-config``.
 
 .. _section-sdh-helpers: