[gimp] tools: fix install-* meson targets.

[Jehan <jehanp src gnome org>]

commit 3bfbf9972ab0ee17b714387dca5d2cd6c6557f74
Author: Jehan <jehan girinstud io>
Date:   Wed Sep 11 18:38:05 2019 +0200

    tools: fix install-* meson targets.
    
    We should not rely on the current working directory, as it looks like
    meson sets it to be the source directory (even when actually in the
    build dir) when running custom target (so it fails).
    
    Instead meson explicitly sets MESON_SOURCE_ROOT and MESON_BUILD_ROOT
    environment variables for us. We should use these. This should work in
    every cases (whether calling from the source or build dir).
    
    Also removing the special-casing for a _build/ directory. This updated
    version is generic and won't assume that you used some generic naming or
    direct subdir under the source (even if many people might use this path
    and name; I, for one, certainly don't!).
    
    See: https://mesonbuild.com/Run-targets.html

 tools/meson_install_subdir.py | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)
---
diff --git a/tools/meson_install_subdir.py b/tools/meson_install_subdir.py
index 2118309f82..da220db1b2 100755
--- a/tools/meson_install_subdir.py
+++ b/tools/meson_install_subdir.py
@@ -34,15 +34,12 @@ class MesonStatus(metaclass = Singleton):
     def get_build_dir(self):
         self.buildroot = None
 
-        cwd = Path(os.getcwd())
+        # Set up by meson.
+        cwd = Path(os.environ['MESON_BUILD_ROOT'])
 
         if (cwd / 'meson-info').exists():
             self.buildroot = cwd
 
-        with cwd / '_build' as _build:
-            if (_build / 'meson-info').exists():
-                self.buildroot = _build
-
         if self.buildroot is None:
             print('Error: build directory was not detected. Are you in it ?')