fix(compat.glfw): the source tree is named by upstream's tag, not by this package's version

`install()` fell back to `"glfw-" .. pkginfo.version()`. That was the same
string for as long as the package had one version; the day it took an ecosystem
segment -- 3.4.0.1, for a pin that moved while upstream did not release -- the
expression asked for `glfw-3.4.0.1/`, which no tarball contains. install() then
moved nothing, and the failure appeared two layers away as
`GLFW/glfw3.h: file not found` in a consumer's test.

A path derived from a version breaks the first time the version means something
the upstream tag does not. The fallback now names the tag, and a source tree
that is missing under both spellings is an error rather than an install that
"succeeds" and leaves a directory with no headers in it.

Found by CI, not locally: `mcpp build` does not compile a member's tests, so the
local check was weaker than the one that caught it.

Author: Sunrisepeak

pkgs/c/compat.glfw.lua

@@ -168,10 +168,35 @@ package = {
 
 import("xim.libxpkg.pkginfo")
 
+-- THE SOURCE TREE IS NAMED BY UPSTREAM'S TAG, NOT BY THIS PACKAGE'S VERSION.
+--
+-- They were the same string for as long as this package had one version, and
+-- the fallback below spelled the directory as `"glfw-" .. pkginfo.version()`.
+-- The day the package took an ecosystem segment -- 3.4.0.1, for a pin that
+-- moved while upstream did not release -- that expression asked for
+-- `glfw-3.4.0.1/`, which no tarball contains. install() then moved nothing and
+-- the failure appeared two layers away, as `GLFW/glfw3.h: file not found` in a
+-- consumer's test.
+--
+-- A path derived from a version is a path that breaks the first time the
+-- version means something the upstream tag does not.
+local UPSTREAM_TAG = "3.4"
+
+import("xim.libxpkg.log")
+
 function install()
     local srcdir = pkginfo.install_file():replace(".tar.gz", "")
     if not os.isdir(srcdir) then
-        srcdir = "glfw-" .. pkginfo.version()
+        srcdir = "glfw-" .. UPSTREAM_TAG
+    end
+    if not os.isdir(srcdir) then
+        -- Loud, because the alternative is an install that "succeeds" and
+        -- leaves an install_dir with no headers in it.
+        log.error("compat.glfw: no source tree at %s; the tarball's top-level "
+                  .. "directory is named by upstream's tag (%s), and neither "
+                  .. "that nor the downloaded name matched",
+                  srcdir, UPSTREAM_TAG)
+        return false
     end
 
     os.tryrm(pkginfo.install_dir())