updated Building.md

doc/Building.md

@@ -141,7 +141,6 @@ So far, the following portions of n2n's code benefit from hardware features:
 AES:               AES-NI
 ChaCha20:          SSE2, SSSE3
 SPECK:             SSE2, SSSE3, AVX2, AVX512, (NEON)
-Pearson Hashing:   AES-NI
 Random Numbers:    RDSEED, RDRND (not faster but more random seed)
 ```
 
@@ -149,6 +148,8 @@ The compilations flags could easily be combined:
 
 `./configure CFLAGS="-O3 -march=native"`.
 
+There are reports of compile errors showing `n2n_seed': random_numbers.c:(.text+0x214): undefined reference to _rdseed64_step'` even though the CPU should support it, see #696. In this case, best solution found so far is to disable `RDSEED` support by adding `-U__RDSEED__` to the `CFLAGS`.
+
 ## OpenSSL Support
 
 Some ciphers' speed can take advantage of OpenSSL support which is disabled by default as the built-in ciphers already prove reasonably fast in most cases. OpenSSL support can be configured using