patch 8.1.2145: cannot map <C-H> when modifyOtherKeys is enabled

Problem:    Cannot map <C-H> when modifyOtherKeys is enabled.
Solution:   Add the <C-H> mapping twice, both with modifier and as 0x08.  Use
            only the first one when modifyOtherKeys has been detected.
diff --git a/src/structs.h b/src/structs.h
index 2d7c4fd..7c0bfce 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -1172,6 +1172,8 @@
     char_u	*m_orig_str;	// rhs as entered by the user
     int		m_keylen;	// strlen(m_keys)
     int		m_mode;		// valid mode
+    int		m_simplified;	// m_keys was simplified, do not use this map
+				// if seenModifyOtherKeys is TRUE
     int		m_noremap;	// if non-zero no re-mapping for m_str
     char	m_silent;	// <silent> used, don't echo commands
     char	m_nowait;	// <nowait> used