The file xfce-panel-macros.h contains extraneous ^M characters (visible through vi):

....
"/opt/Xfce-beta/include/xfce4/libxfcegui4/xfce-heading.h", line 26: warning: syntax error:  empty declaration
"/opt/Xfce-beta/include/xfce4/libxfcegui4/xfce-heading.h", line 80: warning: syntax error:  empty declaration
"/opt/Xfce-beta/include/xfce4/libxfcegui4/xfce-titled-dialog.h", line 26: warning: syntax error:  empty declaration
"/opt/Xfce-beta/include/xfce4/libxfcegui4/xfce-titled-dialog.h", line 73: warning: syntax error:  empty declaration
"../libxfce4panel/xfce-panel-macros.h", line 22: warning: invalid white space character in directive
"../libxfce4panel/xfce-panel-macros.h", line 23: warning: invalid white space character in directive
"../libxfce4panel/xfce-panel-macros.h", line 28: warning: invalid white space character in directive
"../libxfce4panel/xfce-panel-macros.h", line 29: warning: invalid white space character in directive
"../libxfce4panel/xfce-panel-macros.h", line 30: warning: invalid white space character in directive
"../libxfce4panel/xfce-panel-macros.h", line 31: warning: invalid white space character in directive
"../libxfce4panel/xfce-panel-macros.h", line 32: warning: invalid white space character in directive
"../libxfce4panel/xfce-panel-macros.h", line 33: warning: invalid white space character in directive
"../libxfce4panel/xfce-panel-macros.h", line 34: warning: invalid white space character in directive
"../libxfce4panel/xfce-panel-macros.h", line 35: warning: invalid white space character in directive
"../libxfce4panel/xfce-panel-macros.h", line 42: warning: invalid white space character in directive
"../libxfce4panel/xfce-panel-macros.h", line 44: warning: invalid white space character in directive
"frap-icon-entry.h", line 25: warning: syntax error:  empty declaration
"frap-icon-entry.h", line 62: warning: syntax error:  empty declaration
*** Error code 1
The following command caused the error:
failcom='exit 1'; \
for f in x $MAKEFLAGS; do \
  case $f in \
    *=* | --[!k]*);; \
    *k*) failcom='fail=yes';; \
  esac; \
done; \
dot_seen=no; \
target=`echo all-recursive | sed s/-recursive//`; \
list='config                                                             icons  libxfce4panel                                                    panel          plugins                                                          mcs-plugin     po                                                               docs'; for subdir in $list; do \
  echo "Making $target in $subdir"; \
  if test "$subdir" = "."; then \
    dot_seen=yes; \
    local_target="$target-am"; \
  else \
    local_target="$target"; \
  fi; \
  (cd $subdir && make  $local_target) \
  || eval $failcom; \
done; \
if test "$dot_seen" = "no"; then \
  make  "$target-am" || exit 1; \
fi; test -z "$fail"
dmake: Fatal error: Command failed for target `all-recursive'
Current working directory /data/Xfce-beta-src/xfce/xfce4-panel-4.3.90.2svn-22981
*** Error code 1
dmake: Fatal error: Command failed for target `all'