Reimplement apropos -s NUM -S ARCH EXPR by internally converting it to

apropos \( EXPR \) -a 'sec~^NUM$' -a 'arch~^(ARCH|any)$'
in preparation for removal of sec and arch from the mpage table.

Almost no functional change except for the following bonus:
This also makes sure that for cross-section and cross-arch MLINKs,
all of the following work:
apropos -s 1 encrypt
apropos -s 8 encrypt
apropos -s 1 makekey
apropos -s 8 makekey

While here, print error messages about invalid regexps to stderr.

1 files changed, 4 insertions, 2 deletions

diff --git a/mandocdb.c b/mandocdb.c
index c6680163..4b5d8fdb 100644
--- a/mandocdb.c
+++ b/mandocdb.c
@@ -1025,14 +1025,16 @@ mpages_merge(struct mchars *mc, struct mparse *mp, int check_reachable)
 			    mandoc_strdup(mpage->mlinks->name);
 		}
 		putkey(mpage, mpage->sec, TYPE_sec);
-		putkey(mpage, mpage->arch, TYPE_arch);
+		putkey(mpage, '\0' == *mpage->arch ?
+		    "any" : mpage->arch, TYPE_arch);
 
 		for (mlink = mpage->mlinks; mlink; mlink = mlink->next) {
 			if ('\0' != *mlink->dsec)
 				putkey(mpage, mlink->dsec, TYPE_sec);
 			if ('\0' != *mlink->fsec)
 				putkey(mpage, mlink->fsec, TYPE_sec);
-			putkey(mpage, mlink->arch, TYPE_arch);
+			putkey(mpage, '\0' == *mlink->arch ?
+			    "any" : mlink->arch, TYPE_arch);
 			putkey(mpage, mlink->name, TYPE_Nm);
 		}