Problem with MesaLib based ports

Whilst upgrading my system to xorg 7.2, I found that I sometimes had to 
'mkdir lib' in the extracted tree for ports using the MesaLib distfile. 
A number of ports seem to be affected by this.

The latest breakage was with yesterday's graphics/libGL port update:
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cc -c -I. -I../../../include -I../../../include/GL/internal 
-I../../../src/mesa/main -I../../../src/mesa/glapi -O2 
-fno-strict-aliasing -pipe  -I/usr/local/include 
-I/usr/local/include/drm `pkg-config --cflags libdrm` 
-I/usr/local/include -O2 -fno-strict-aliasing -pipe  
-I/usr/local/include -I/usr/local/include/drm -Wall -O2 
-fno-strict-aliasing -pipe  -I/usr/local/include 
-I/usr/local/include/drm  -Wmissing-prototypes -std=c99 -Wundef 
-ffast-math -DUSE_X86_ASM -DUSE_MMX_ASM -DUSE_3DNOW_ASM -DUSE_SSE_ASM 
-I/usr/local/include -DPTHREADS -DUSE_EXTERNAL_DXTN_LIB=1 
-DIN_DRI_DRIVER -DGLX_DIRECT_RENDERING -DGLX_INDIRECT_RENDERING 
-DHAVE_ALIAS -DHAVE_POSIX_MEMALIGN -DXF86VIDMODE -D_REENTRANT 
-UIN_DRI_DRIVER -DDEFAULT_DRIVER_DIR=\"/usr/local/lib/dri\"  
../../../src/mesa/x86/glapi_x86.S -o ../../../src/mesa/x86/glapi_x86.o
../../../bin/mklib -o GL -linker 'cc' \
                -major 1 -minor 2  \
                -install ../../../lib -L/usr/local/lib -lX11 -lXext 
-lXxf86vm -lXdamage -lXfixes -lm -pthread `pkg-config --libs libdrm` 
glcontextmodes.o clientattrib.o compsize.o eval.o glxcmds.o glxext.o 
glxextensions.o indirect.o indirect_init.o indirect_size.o 
indirect_window_pos.o indirect_transpose_matrix.o 
indirect_vertex_array.o indirect_vertex_program.o pixel.o pixelstore.o 
render2.o renderpix.o single2.o singlepix.o vertarr.o xfont.o 
glx_pbuffer.o glx_query.o glx_texture_compression.o dri_glx.o XF86dri.o 
../../../src/mesa/main/dispatch.o ../../../src/mesa/glapi/glapi.o 
../../../src/mesa/glapi/glthread.o ../../../src/mesa/x86/glapi_x86.o
mklib: Making FreeBSD shared library:  libGL.so.1
mklib: Installing libGL.so.1 libGL.so in ../../../lib
usage: mv [-f | -i | -n] [-v] source target
       mv [-f | -i | -n] [-v] source ... directory
gmake[3]: *** [../../../lib/libGL.so] Error 64
gmake[3]: Leaving directory 
`/usr/ports/graphics/libGL/work/Mesa-7.0/src/glx/x11'
gmake[2]: *** [subdirs] Error 1
gmake[2]: Leaving directory `/usr/ports/graphics/libGL/work/Mesa-7.0/src'
gmake[1]: *** [default] Error 1
gmake[1]: Leaving directory `/usr/ports/graphics/libGL/work/Mesa-7.0'
gmake: *** [freebsd-dri-x86] Error 2
*** Error code 2

Stop in /usr/ports/graphics/libGL.
%%%

If I 'mkdir lib' in /usr/ports/graphics/libGL/work/Mesa-7.0 I do not see 
this failure.

BMS