[wip/MPC] Add a patch to fix incorrect use of substring on cmake < 2.8

MPC/distinfo

@@ -2,3 +2,4 @@ SHA1 (MPC-1.0.tar.gz) = a45fe2e16fb0d93673b014ddff38c074218a0517
 RMD160 (MPC-1.0.tar.gz) = 0383006d9f413d201b7b3dc6da8d6169beaf5a4e
 Size (MPC-1.0.tar.gz) = 803443 bytes
 SHA1 (patch-aa) = 66e1c649e6adbb86e6c49256ce8abcc4293f2bc5
+SHA1 (patch-ab) = 6883ab33b9e2e1a469c872d6cbb05ca6c5dc43e3

MPC/patches/patch-ab

+[CMakeLists.txt] Fix it for cmake < 2.8
+
+cmake 2.8 allows a length of -1 in substring, but not previous
+version.  So do manually the size computation before calling
+substring !
+
+--- MPC/CMakeLists.txt
++++ MPC/CMakeLists.txt
+@@ -5,7 +5,9 @@ set(PACKAGE_VERSION 1.0)
+ 
+ macro(GET_LIBRARY_NAME LIBRARY_FULL LIBRARY_NAME)
+ 	get_filename_component(LIBRARY_BASE ${LIBRARY_FULL} NAME_WE)
+-	string(SUBSTRING ${LIBRARY_BASE} 3 -1 PIPO)
++	string(LENGTH ${LIBRARY_BASE} LEN)
++	math(EXPR SUB_LEN "${LEN} - 3")
++	string(SUBSTRING ${LIBRARY_BASE} 3 ${SUB_LEN} PIPO)
+ 	set(${LIBRARY_NAME} ${PIPO})
+ endmacro()
+