liblzma: Add more uses of lzma_memcmplen() to the normal mode of LZMA.

This gives a tiny encoder speed improvement. This could have been done
in 2014 after the commit 544aaa3d13554e8640f9caf7db717a96360ec0f6 but
it was forgotten.

src/liblzma/lzma/lzma_encoder_optimum_normal.c

@@ -636,9 +636,10 @@
 		uint32_t len_test_2 = len_test + 1;
 		const uint32_t limit = my_min(buf_avail_full,
 				len_test_2 + nice_len);
-		for (; len_test_2 < limit
-				&& buf[len_test_2] == buf_back[len_test_2];
-				++len_test_2) ;
+		// NOTE: len_test_2 may be greater than limit so the call to
+		// lzma_memcmplen() must be done conditionally.
+		if (len_test_2 < limit)
+			len_test_2 = lzma_memcmplen(buf, buf_back, len_test_2, limit);
 
 		len_test_2 -= len_test + 1;
 
@@ -732,9 +733,12 @@
 				const uint32_t limit = my_min(buf_avail_full,
 						len_test_2 + nice_len);
 
-				for (; len_test_2 < limit &&
-						buf[len_test_2] == buf_back[len_test_2];
-						++len_test_2) ;
+				// NOTE: len_test_2 may be greater than limit
+				// so the call to lzma_memcmplen() must be
+				// done conditionally.
+				if (len_test_2 < limit)
+					len_test_2 = lzma_memcmplen(buf, buf_back,
+							len_test_2, limit);
 
 				len_test_2 -= len_test + 1;