install_update_dovecot-2.4.sh: change calculation of numbers of cpus.

install_update_dovecot-2.4.sh

@@ -2361,7 +2361,13 @@ done
 
 ## - Let make use multiple cores (-j<number of cores +1>)
 ## -
-export MAKEFLAGS=-j$(expr `grep  "^processor" /proc/cpuinfo | sort -u | wc -l` - 1)
+#export MAKEFLAGS=-j$(expr `grep  "^processor" /proc/cpuinfo | sort -u | wc -l` - 1)
+CPUS=$(nproc)
+if (( CPUS > 1 )); then
+    export MAKEFLAGS="-j$((CPUS - 1))"
+else
+    export MAKEFLAGS="-j1"
+fi
 
 
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