Fix aom.pc generation.

$GIT_EXECUTABLE was being passed as the
value of CMAKE_INSTALL_PREFIX to pkg_config.cmake. Pass
$CMAKE_INSTALL_PREFIX as intended.

BUG=aomedia:814

Change-Id: I86126f472447eaa6a2196dca3a8c68fb4de9415a

CMakeLists.txt

@@ -209,7 +209,7 @@ if (NOT MSVC)
     COMMAND ${CMAKE_COMMAND}
     ARGS -DAOM_CONFIG_DIR=${AOM_CONFIG_DIR}
       -DAOM_ROOT=${AOM_ROOT}
-      -DCMAKE_INSTALL_PREFIX=${GIT_EXECUTABLE}
+      -DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}
       -DCMAKE_PROJECT_NAME=${CMAKE_PROJECT_NAME}
       -DCONFIG_MULTITHREAD=${CONFIG_MULTITHREAD}
       -DHAVE_PTHREAD_H=${HAVE_PTHREAD_H}

build/cmake/aom_configure.cmake

@@ -408,7 +408,7 @@ if (NOT MSVC)
     COMMAND ${CMAKE_COMMAND}
     -DAOM_CONFIG_DIR=${AOM_CONFIG_DIR}
     -DAOM_ROOT=${AOM_ROOT}
-    -DCMAKE_INSTALL_PREFIX=${GIT_EXECUTABLE}
+    -DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}
     -DCMAKE_PROJECT_NAME=${CMAKE_PROJECT_NAME}
     -DCONFIG_MULTITHREAD=${CONFIG_MULTITHREAD}
     -DHAVE_PTHREAD_H=${HAVE_PTHREAD_H}