[3.12] gh-75371: reformat Makefile.pre.in to accommodate for empty FRAMEWORKALTINSTAL...

[3.12] gh-75371: reformat Makefile.pre.in to accommodate for empty FRAMEWORKALTINSTALLLAST (GH-107035) (#107049)

gh-75371: reformat Makefile.pre.in to accommodate for empty FRAMEWORKALTINSTALLLAST (GH-107035)

in the case of an empty FRAMEWORKALTINSTALLLAST, this patch prevents leaving
an astray linebreak and two tabs in the resulting Makefile.

Before change:
```
.PHONY: commoninstall
commoninstall:  check-clean-src  \
		altbininstall libinstall inclinstall libainstall \
		sharedinstall altmaninstall \

```

After change (with empty FRAMEWORKALTINSTALLLAST):
```
.PHONY: commoninstall
commoninstall:  check-clean-src  \
		altbininstall libinstall inclinstall libainstall \
		sharedinstall altmaninstall
```
(cherry picked from commit 9c38206925246ab919cf558ac069ae9458720ba7)

Co-authored-by: Moritz Neeb <nt4u@kpvn.de>