Util/StringUtil: add StringStartsWith()

Replaces GLib's g_str_has_prefix().

src/util/StringUtil.cxx

@@ -22,6 +22,7 @@
 #include "ASCII.hxx"
 
 #include <assert.h>
+#include <string.h>
 
 const char *
 strchug_fast(const char *p)
@@ -32,6 +33,13 @@ strchug_fast(const char *p)
 	return p;
 }
 
+bool
+StringStartsWith(const char *haystack, const char *needle)
+{
+	const size_t length = strlen(needle);
+	return memcmp(haystack, needle, length) == 0;
+}
+
 bool
 string_array_contains(const char *const* haystack, const char *needle)
 {

src/util/StringUtil.hxx

@@ -40,6 +40,10 @@ strchug_fast(char *p)
 	return const_cast<char *>(strchug_fast((const char *)p));
 }
 
+gcc_pure
+bool
+StringStartsWith(const char *haystack, const char *needle);
+
 /**
  * Checks whether a string array contains the specified string.
  *