Fix regression: -bp should check BuildRequires

Some source packages assume that BuildRequires are installed before
%prep is executed.  For example, `openssh` BuildRequires `automake` and
runs `autoreconf` in %prep.

Prior to 11c56d5 `rpmbuild -bp` checked BuildRequires and printed a
helpful error message if there were any missing dependencies.  Since
that commit, `rpmbuild -bp` skips the BuildRequires check, which can
lead to misleading errors in %prep.

This commit restores the BuildRequires check in `rpmbuild -bp`.

Co-authored-by: Florian Festi <ffesti@redhat.com>

rpmbuild.c

@@ -674,6 +674,9 @@ int main(int argc, char *argv[])
 	/* fallthrough */
     case 'p':
 	ba->buildAmount |= RPMBUILD_PREP;
+	if (!noDeps) {
+	    ba->buildAmount |= RPMBUILD_CHECKBUILDREQUIRES;
+	}
 	break;
     case 'l':
 	ba->buildAmount |= RPMBUILD_FILECHECK;