tests: fix targets with no sources

This was never supposed to be possible, so stop doing it.

test cases/common/215 source set realistic example/meson.build

@@ -30,6 +30,7 @@ subdir('devices')
 if meson.is_unity()
   specific.add_all(common)
   common = ss.source_set()
+  common.add(files('dummy.cpp'))
 endif
 
 common_lib = static_library('common', common.all_sources(),

test cases/common/44 pkgconfig-gen/dependencies/dummy.c

@@ -0,0 +1,3 @@
+int dummy(void) {
+    return 0;
+}

test cases/common/44 pkgconfig-gen/dependencies/meson.build

@@ -5,7 +5,7 @@ pkgg = import('pkgconfig')
 # libmain internally use libinternal and expose libexpose in its API
 exposed_lib = shared_library('libexposed', 'exposed.c')
 internal_lib = shared_library('libinternal', 'internal.c')
-main_lib = both_libraries('libmain', link_with : [exposed_lib, internal_lib])
+main_lib = both_libraries('libmain', 'dummy.c', link_with : [exposed_lib, internal_lib])
 custom_lib = shared_library('custom', 'custom.c')
 
 pkgg.generate(exposed_lib)
@@ -55,7 +55,7 @@ pkgg.generate(
 
 # Verify that if we promote internal_lib as public dependency, it comes after
 # the main library.
-main_lib2 = both_libraries('libmain2', link_with : internal_lib)
+main_lib2 = both_libraries('libmain2', 'dummy.c', link_with : internal_lib)
 pkgg.generate(main_lib2,
   libraries : internal_lib,
   filebase : 'pub-lib-order',

test cases/common/44 pkgconfig-gen/meson.build

@@ -153,7 +153,7 @@ ct = custom_target('stat3',
   output: fs.name(outfile),
   command: [python, '-c', script],
 )
-simple6 = library('simple6', link_with: ct)
+simple6 = library('simple6', 'dependencies/dummy.c', link_with: ct)
 pkgg.generate(simple6)
 
 # implicit variables

test cases/frameworks/28 gir link order 2/samelibname/meson.build

@@ -1,5 +1,5 @@
 samelibname = shared_library(
   'sample',
-  sources : [],
+  sources : 'dummy.c',
   install : false,
 )

test cases/unit/52 pkgconfig static link order/meson.build

@@ -1,7 +1,7 @@
 project('link order test', 'c')
 
-dep = library('dependency', [])
-lib = static_library('something', [], link_with: dep)
+dep = library('dependency', 'dummy.c')
+lib = static_library('something', 'dummy.c', link_with: dep)
 
 import('pkgconfig').generate(
   name: 'libsomething',