Rebuild when build-time/run-time deps are upgraded.

man/emerge.1

 .TH "EMERGE" "1" "Apr 2011" "Portage VERSION" "Portage"
 .SH "NAME"
 emerge \- Command\-line interface to the Portage system
 .SH "SYNOPSIS"
 .TP
 .BR emerge
 [\fIoptions\fR] [\fIaction\fR] [\fIebuild\fR | \fItbz2file\fR | \fIfile\fR | \fI@set\fR | \fIatom\fR] ...
 .TP
 .BR emerge
 \fB\-\-sync\fR | \fB\-\-version\fR
@@ skipping 471 matching lines @@
 may have changed.
 .TP
 .BR "\-\-nospinner"
 Disables the spinner for the session.  The spinner is active when the
 terminal device is determined to be a TTY.  This flag disables it regardless.
 .TP
 .BR "\-\-nousepkg\-atoms " ATOMS
 A space separated list of package names or slot atoms. Emerge will ignore
 matching binary packages.
 .TP
+.BR "\-\-norebuild\-atoms " ATOMS
+A space separated list of package names or slot atoms. Emerge will not rebuild
+matching packages due to \fB\-\-rebuild\fR.
+.TP
 .BR "\-\-oneshot " (\fB\-1\fR)
 Emerge as normal, but do not add the packages to the world file
 for later updating.
 .TP
 .BR "\-\-onlydeps " (\fB\-o\fR)
 Only merge (or pretend to merge) the dependencies of the packages
 specified, not the packages themselves.
 .TP
 .BR "\-\-package\-moves [ y | n ]"
 Perform package moves when necessary. This option
@@ skipping 29 matching lines @@
 .BR "\-\-quiet\-build [ y | n ]"
 Redirect all build output to logs alone, and do not
 display it on stdout.
 .TP
 .BR \-\-quiet\-unmerge\-warn
 Disable the warning message that's shown prior to
 \fB\-\-unmerge\fR actions. This option is intended
 to be set in the \fBmake.conf\fR(5)
 \fBEMERGE_DEFAULT_OPTS\fR variable.
 .TP
+.BR "\-\-rebuild [ y | n ]"
+Rebuild packages when dependencies that are used at both build-time and
+run-time are upgraded.
+.TP
 .BR "\-\-rebuilt\-binaries [ y | n ]"
 Replace installed packages with binary packages that have
 been rebuilt. Rebuilds are detected by comparison of
 BUILD_TIME package metadata. This option is enabled
 automatically when using binary packages
 (\fB\-\-usepkgonly\fR or \fB\-\-getbinpkgonly\fR) together with
 \fB\-\-update\fR and \fB\-\-deep\fR.
 .TP
 .BR "\-\-rebuilt\-binaries\-timestamp=TIMESTAMP"
 This option modifies emerge's behaviour only if
@@ skipping 418 matching lines @@
 .BR ebuild (1),
 .BR ebuild (5),
 .BR make.conf (5),
 .BR color.map (5),
 .BR portage (5)
 .LP
 A number of helper applications reside in \fI/usr/lib/portage/bin\fR.
 .LP
 The \fBapp\-portage/gentoolkit\fR package contains useful scripts such as 
 \fBequery\fR (a package query tool).