[gentoo-user] Puzzled with duration of chromium emerge under profile 17.0

[Mick]

I discovered that building Chromium with gcc-6.4.0 is taking an inordinately 
longer time on a laptop with 1st gen i7 and 4G of RAM, e.g.: 

     Wed Sep 27 17:36:53 2017 >>> www-client/chromium-61.0.3163.100
       merge time: 6 hours, 40 minutes and 50 seconds.

     Thu Nov  9 17:44:58 2017 >>> www-client/chromium-62.0.3202.89
       merge time: 8 hours, 12 minutes and 30 seconds.

-->switch to gcc-6.4.0

     Mon Dec  4 11:39:36 2017 >>> www-client/chromium-62.0.3202.89
       merge time: 20 hours, 2 minutes and 4 seconds.

     Wed Dec  6 18:41:13 2017 >>> www-client/chromium-62.0.3202.94
       merge time: 22 hours, 47 minutes and 35 seconds.


but not so on another older and lesser Intel(R) Core(TM)2 Duo CPU P7550  @ 
2.26GHz, also with 4G RAM:

     Wed Sep 27 22:25:32 2017 >>> www-client/chromium-61.0.3163.100
       merge time: 11 hours, 46 minutes and 18 seconds.

     Thu Nov  9 22:09:59 2017 >>> www-client/chromium-62.0.3202.89
       merge time: 13 hours, 16 minutes and 41 seconds.

-->switch to gcc-6.4.0

     Sat Dec  2 21:00:59 2017 >>> www-client/chromium-62.0.3202.89
       merge time: 15 hours, 35 minutes and 50 seconds.

     Mon Dec  4 03:44:12 2017 >>> www-client/chromium-62.0.3202.94
       merge time: 15 hours, 40 minutes and 18 seconds.


Any idea why this is happening?  I attach emerge info of the i7 in case you 
can spot something which may be causing this exponential increase in emerge 
times.  BTW, on the i7 I had to increase swap because the 4,200,960 KiB swap 
partition was not enough to complete the compilation of version 62.0.3202.89, 
even after I shut down all applications and exited X.  O_O

-- 
Regards,
Mick