The shadows.DONE target in a number of xorg components looks a bit like this
(this one's from bitmap; sometimes it's $(LIB_MAN_SUFFIX) rather than
$(APP_MAN_SUFFIX), as in e.g. libxext):

shadows.DONE:
        -rm -f $(man_shadows:=.@APP_MAN_SUFFIX@)
        (for i in $(man_shadows:=.@APP_MAN_SUFFIX@) ; do \
         echo .so man$(APP_MAN_SUFFIX)/bitmap.$(APP_MAN_SUFFIX) > $$i; \
         done)

This is incorrect, because the XORG_MANPAGE_SECTIONS macro reads as follows:

if test x$APP_MAN_SUFFIX = x    ; then
    case $host_os in
        linux*) APP_MAN_SUFFIX=1x ;;
        *)      APP_MAN_SUFFIX=1  ;;
    esac
fi
if test x$APP_MAN_DIR = x    ; then
    case $host_os in
        linux*) APP_MAN_DIR='$(mandir)/man1' ;;
        *)      APP_MAN_DIR='$(mandir)/man$(APP_MAN_SUFFIX)' ;;
    esac
fi

Thus on Linux we're not installing into man$(APP_MAN_SUFFIX), we're installing
into man1 (or man3 in the case of libraries), and the shadows.DONE code creates
an incorrect .so link which will cause manual page readers to be unable to read
the shadow pages. (I maintain man-db, which is one such tool.)

I suggest changes along the lines of the following, in bitmap:

--- bitmap-1.0.1.orig/Makefile.am
+++ bitmap-1.0.1/Makefile.am
@@ -139,5 +139,5 @@
 shadows.DONE:
        -rm -f $(man_shadows:=.@APP_MAN_SUFFIX@)
        (for i in $(man_shadows:=.@APP_MAN_SUFFIX@) ; do \
-        echo .so man$(APP_MAN_SUFFIX)/bitmap.$(APP_MAN_SUFFIX) > $$i; \
+        echo .so $(notdir $(APP_MAN_DIR))/bitmap.$(APP_MAN_SUFFIX) > $$i; \
         done)

... and the following, in libxext:

--- libxext-1.0.0.orig/man/Makefile.am
+++ libxext-1.0.0/man/Makefile.am
@@ -48,13 +48,13 @@
 shadows.DONE:
        -rm -f $(all_aliases:=.@LIB_MAN_SUFFIX@)
        (for i in $(XShape_man_aliases:=.@LIB_MAN_SUFFIX@) ; do \
-       echo .so man$(LIB_MAN_SUFFIX)/XShape.$(LIB_MAN_SUFFIX) > $$i; \
+       echo .so $(notdir $(LIB_MAN_DIR))/XShape.$(LIB_MAN_SUFFIX) > $$i; \
        done)
        (for i in $(Xmbuf_man_aliases:=.@LIB_MAN_SUFFIX@) ; do \
-       echo .so man$(LIB_MAN_SUFFIX)/Xmbuf.$(LIB_MAN_SUFFIX) > $$i; \
+       echo .so $(notdir $(LIB_MAN_DIR))/Xmbuf.$(LIB_MAN_SUFFIX) > $$i; \
        done)
        (for i in $(Xevi_man_aliases:=.@LIB_MAN_SUFFIX@) ; do \
-       echo .so man$(LIB_MAN_SUFFIX)/Xevi.$(LIB_MAN_SUFFIX) > $$i; \
+       echo .so $(notdir $(LIB_MAN_DIR))/Xevi.$(LIB_MAN_SUFFIX) > $$i; \
        done)
        touch shadows.DONE

However, there are probably far too many affected components for me to attach
individual patches for each, and I don't have a full checkout of the modular
tree at the moment. If it isn't easy for somebody who does have such a checkout
to go through and fix all instances of this in one sweep, let me know and I'll
try to produce a patch.