add_library: Test invalid GLOBAL INTERFACE signature.

This has to be tested separately from the invalid_signature test because
target sources are evaluate at a later time, and earlier errors in the
invalid_signature test cause early exit.

Tests/RunCMake/interface_library/RunCMakeTest.cmake

@@ -5,5 +5,6 @@ run_cmake(target_commands)
 run_cmake(no_shared_libs)
 run_cmake(whitelist)
 run_cmake(invalid_signature)
+run_cmake(global-interface)
 run_cmake(genex_link)
 run_cmake(add_dependencies)

Tests/RunCMake/interface_library/global-interface-result.txt

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

Tests/RunCMake/interface_library/global-interface-stderr.txt

@@ -0,0 +1,9 @@
+CMake Error at global-interface.cmake:2 \(add_library\):
+  Cannot find source file:
+
+    GLOBAL
+
+  Tried extensions \.c \.C \.c\+\+ \.cc \.cpp \.cxx \.m \.M \.mm \.h \.hh \.h\+\+ \.hm \.hpp
+  \.hxx \.in \.txx
+Call Stack \(most recent call first\):
+  CMakeLists.txt:3 \(include\)

Tests/RunCMake/interface_library/global-interface.cmake

@@ -0,0 +1,2 @@
+
+add_library(iface GLOBAL INTERFACE)

Tests/RunCMake/interface_library/invalid_signature.cmake

@@ -16,5 +16,5 @@ add_library(iface15 ALIAS INTERFACE)
 add_library(iface16 INTERFACE INTERFACE)
 add_library(iface17 INTERFACE EXCLUDE_FROM_ALL)
 add_library(iface18 EXCLUDE_FROM_ALL INTERFACE)
-add_library(iface19 GLOBAL INTERFACE)
+# add_library(iface19 GLOBAL INTERFACE) Tested separately
 add_library(iface20 INTERFACE GLOBAL)