Introduce add_compile_options command.

This command is similar to add_definitions, in that it affects
the compile options of all targets which follow it. The implementation
is similar to the implementation of the include_directories command,
in that it is based on populating a COMPILE_OPTIONS directory property
and using that to initialize the same property on targets.

Unlike the include_directories command however, the add_compile_options
command does not affect previously defined targets. That is, in
the following code, foo will not be compiled with -Wall, but bar
will be:

 add_library(foo ...)
 add_compile_options(-Wall)
 add_library(bar ...)

1 files changed, 11 insertions, 0 deletions

diff --git a/Tests/CMakeCommands/add_compile_options/main.cpp b/Tests/CMakeCommands/add_compile_options/main.cpp
new file mode 100644
index 0000000..2bb20ac
--- /dev/null
+++ b/Tests/CMakeCommands/add_compile_options/main.cpp
@@ -0,0 +1,11 @@
+
+#ifdef DO_GNU_TESTS
+#  ifndef TEST_OPTION
+#  error Expected TEST_OPTION
+#  endif
+#endif
+
+int main(void)
+{
+  return 0;
+}