cmake: Allow RUNPREFIX to be specified at build time.

The code previously always assigned CMAKE_INSTALL_PREFIX to RUNPREFIX,
the location that the mythfrontend believes is its location.  Add a
new option, MYTH_RUN_PREFIX, allowing this variable to be specified
when the build tree is created.  This is analogous to the configure
--runprefix option.

Refs: #980
(cherry picked from commit 31ea30c)

cmake/MythOptions.cmake

@@ -21,6 +21,11 @@ set(MYTH_DEFAULT_LIBS_PREFIX
     CACHE PATH
           "Default library install prefix if not specified on the command line."
 )
+set(MYTH_RUN_PREFIX
+    ""
+    CACHE PATH
+          "The prefix where MythTV is expected to be at runtime.  This may differ from MYTH_DEFAULT_PREFIX or CMAKE_INSTALL_PREFIX for packagers."
+)
 
 # Location for downloaded tarballs.
 #

mythtv/CMakeLists.txt

@@ -71,6 +71,9 @@ include(VersionInformation)
 #
 message(STATUS "Including user overrides ${MYTH_USER_OVERRIDES2}")
 include(${MYTH_USER_OVERRIDES2} OPTIONAL)
+if(NOT MYTH_RUN_PREFIX)
+  set(MYTH_RUN_PREFIX ${CMAKE_INSTALL_PREFIX})
+endif()
 
 #
 # Inject code from cmake provided modules

mythtv/cmake/PrintConfig.cmake

@@ -60,7 +60,7 @@ if(NOT "${quiet}" STREQUAL "yes")
   message_vrbl("Ccache                  " CCACHE_FOUND)
   message_vrbl("DistCC                  " DISTCC_FOUND)
   message("install prefix            ${CMAKE_INSTALL_PREFIX}")
-  message("runtime prefix            ${CMAKE_INSTALL_PREFIX}")
+  message("runtime prefix            ${MYTH_RUN_PREFIX}")
   message("")
   # ~~~
   # if( CPU_OVERRIDE AND test x"$cpu" != x"generic")

mythtv/libs/libmythbase/CMakeLists.txt

@@ -266,7 +266,7 @@ set_source_files_properties(
   mythdirs.cpp
   PROPERTIES
     COMPILE_DEFINITIONS
-    "RUNPREFIX=\"${CMAKE_INSTALL_PREFIX}\";LIBDIRNAME=\"${CMAKE_INSTALL_LIBDIR}\""
+    "RUNPREFIX=\"${MYTH_RUN_PREFIX}\";LIBDIRNAME=\"${CMAKE_INSTALL_LIBDIR}\""
 )
 target_include_directories(
   mythbase