[gimp] build: build OpenEXR plug-in.

[Jehan <jehanp src gnome org>]

commit ffc7db84d1834a8720fcf2b6109b97c3a0e3adf7
Author: Jehan <jehan girinstud io>
Date:   Tue Apr 21 14:47:51 2020 +0200

    build: build OpenEXR plug-in.
    
    libopenexr was installed, but pkg-config was failing because of missing
    dependency:
    ```
    $ x86_64-w64-mingw32-pkg-config --modversion OpenEXR
    Package IlmBase was not found in the pkg-config search path.
    Perhaps you should add the directory containing `IlmBase.pc'
    to the PKG_CONFIG_PATH environment variable
    Package 'IlmBase', required by 'OpenEXR', not found
    ```
    
    Looks like there may be a dependency bug in the openexr package in
    Msys2. Anyway let's just add ilmbase and get this to be detected
    correctly.

 build/windows/crossbuild-gitlab-ci/build-deps.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/build/windows/crossbuild-gitlab-ci/build-deps.sh 
b/build/windows/crossbuild-gitlab-ci/build-deps.sh
index 0394e54b4e..865d051c48 100644
--- a/build/windows/crossbuild-gitlab-ci/build-deps.sh
+++ b/build/windows/crossbuild-gitlab-ci/build-deps.sh
@@ -39,6 +39,6 @@ crossroad install appstream-glib              \
                   libmypaint mypaint-brushes  \
                   libwebp                     \
                   libwmf                      \
-                  openexr                     \
+                  openexr ilmbase             \
                   poppler poppler-data        \
                   xpm-nox