treewide: internally avoid deprecated machine file uses of "pkgconfig"

We support this in a machine file:

```
[binaries]
pkgconfig = 'pkg-config'
pkg-config = 'pkg-config'
```

and you can use either one, because internally we look up both. If you
only set *one* of them, this plays awkwardly with setting $PKG_CONFIG,
since we don't know which one you set in the machine file and the
*other* one will be initialized from the environment instead.

In commit 22df45a31981874310a78dde0df59a6a7c5ebb29 we changed program
lookup of config-tool style dependencies to use the regular tool names
and only fall back on the strange internal names. This affected the
pkg-config class too.

The result is that instead of preferring `pkgconfig =` followed by
$PKG_CONFIG followed by `pkg-config =`, we inverted the lookup order.
This is a good idea anyway, because now it behaves consistently with
`find_program('pkg-config')`.

Unfortunately, we documented the wrong name in a bunch of places, and
also used the wrong name in various testsuite bits, which meant that if
you set $PKG_CONFIG and then ran the testsuite, it would fail.

Correct these references, because they are buggy.

One test case expected to find_program() a native copy for convenience
of testing against natively installed glib. Force it to resolve a native
copy.

1 files changed, 3 insertions, 3 deletions

diff --git a/docs/markdown/Machine-files.md b/docs/markdown/Machine-files.md
index 9e4b0c2..c300769 100644
--- a/docs/markdown/Machine-files.md
+++ b/docs/markdown/Machine-files.md
@@ -90,7 +90,7 @@ arch = 'aarch64-linux-gnu'
 c = arch + '-gcc'
 cpp = arch + '-g++'
 strip = arch + '-strip'
-pkgconfig = arch + '-pkg-config'
+pkg-config = arch + '-pkg-config'
 ...
 ```
 
@@ -165,7 +165,7 @@ c_ld = 'gold'
 cpp_ld = 'gold'
 ar = '/usr/i586-mingw32msvc/bin/ar'
 strip = '/usr/i586-mingw32msvc/bin/strip'
-pkgconfig = '/usr/bin/i586-mingw32msvc-pkg-config'
+pkg-config = '/usr/bin/i586-mingw32msvc-pkg-config'
 ```
 
 An incomplete list of internally used programs that can be overridden
@@ -179,7 +179,7 @@ here is:
 - libwmf-config
 - llvm-config
 - pcap-config
-- pkgconfig
+- pkg-config
 - sdl2-config
 - wx-config (or wx-3.0-config or wx-config-gtk)