Make the gtest dependency optional.

This is needed to build in flatpak.

.gitignore

@@ -1 +1,2 @@
 .idea/
+*.swp

subprojects/.gitignore

@@ -0,0 +1 @@
+gtest

test/meson.build

@@ -7,13 +7,18 @@ tests = [
 ]
 
 
-gtest_dep = dependency('gtest', main:true, fallback: ['gtest', 'gtest_dep'])
+gtest_dep = dependency('gtest',
+                       main:true,
+                       fallback: ['gtest', 'gtest_dep'],
+                       required:false)
 
-foreach test_name : tests
-    test_exe = executable(test_name, [test_name+'.cpp'],
-                          link_with : kiwixlib,
-                          link_args: extra_link_args,
-                          dependencies : all_deps + [gtest_dep],
-                          build_rpath : '$ORIGIN')
-    test(test_name, test_exe)
-endforeach
+if gtest_dep.found()
+    foreach test_name : tests
+        test_exe = executable(test_name, [test_name+'.cpp'],
+                              link_with : kiwixlib,
+                              link_args: extra_link_args,
+                              dependencies : all_deps + [gtest_dep],
+                             build_rpath : '$ORIGIN')
+        test(test_name, test_exe)
+    endforeach
+endif