Re: [PR REVIEW] cmt: update to 1.18 and make it buildable

[kruceter <kruceter@users.noreply.github.com>]

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New review comment by kruceter on void-packages repository

https://github.com/void-linux/void-packages/pull/39583#discussion_r1064050817

Comment:
My apologies for the delay.

> I don't think sed would even be necessary when make_use_env wouldn't be set.

cmt's makefile defines CFLAGS and CXXFLAGS with `=` which completely overrides external variables as far as I can tell.

Here is what the makefile contains:
```
CFLAGS		=	$(INCLUDES) -Wall -Werror -O2 -fPIC
CXXFLAGS	=	$(CFLAGS)
PLUGIN_LIB	=	../plugins/cmt.so
```

> But both of these approaches have a flaw: they remove the `-fPIC` flag from `CFLAGS`.

That would be my fault for overlooking this.

Using sed to stuff it with void's flags just because `-fPIC` is present there looks overcomplicated and unnecessary.

In this case I can suggest the following (I forgot `vsed` must be used instead of `sed`):

```diff
diff --git a/srcpkgs/cmt/template b/srcpkgs/cmt/template
index a07ca8a069..6c676b62b9 100644
--- a/srcpkgs/cmt/template
+++ b/srcpkgs/cmt/template
@@ -14,9 +14,9 @@ distfiles="https://www.ladspa.org/download/${pkgname}_${version}.tgz"
 checksum=a82f8636de1f4ada386a199a017a9cd775a49b49e716b11e8dd3f723c93df6ca
 
 post_extract() {
-	sed -e "/^CFLAGS/ s/-O2/${CFLAGS}/" \
+	vsed -e "s,^\(CFLAGS.*\)=,\1+=," \
 	  -e 's|-Werror||g' \
-	  -i "${wrksrc}/src/Makefile"
+	  -i "${build_wrksrc}/Makefile"
 }
 
 do_install() {
```

`=` is substituted with `+=`, thus making externally defined `CFLAGS` and `CXXFLAGS` usable.

`make_use_env` now has its use here unlike earlier:
```markdown
This build style tries to compensate for makefiles
that do not respect environment variables, so well written makefiles, those
that do such things as append (`+=`) to variables, should have `make_use_env`
set in the body of the template.
```

With this approach only two lines have to be changed without meddling with upstream flags.

> `-fPIC` could be added to `make_build_args`

Based on my previous answer (I have had overlooked this flag for reasons unknown), I believe it should be left in the makefile since the fix above allows to use void's flags with those in the makefile together without that ugly hack.