syscall_filter: Fix whitespace handling.

Typos of the form "syscallname :1" were triggering compilation
failures. Fix by stripping |syscall_name| before looking up the
syscall.

Bug: 37753889
Test: New unit test.
Change-Id: I653b8f1f9995a5269129ccca330a3ea2e7245722
diff --git a/syscall_filter.c b/syscall_filter.c
index 9a66d17..5a3ef21 100644
--- a/syscall_filter.c
+++ b/syscall_filter.c
@@ -550,6 +550,7 @@
 			goto free_line;
 		}
 
+		syscall_name = strip(syscall_name);
 		int nr = lookup_syscall(syscall_name);
 		if (nr < 0) {
 			warn("compile_file: nonexistent syscall '%s'",