exports: use CMAKE_SHARED_LIBRARY_PREFIX to determine lib name

f19edfa95f8dc9fa596282a210757e4d6d0cd490 broke for some people who used
libaom.dll as the linked library as the def file caused the linker to
produce aom.dll instead

Signed-off-by: Christopher Degawa <christopher.degawa@intel.com>
Change-Id: I9040de491d9df5a9434e7874ed8b6e8d1c82a203

build/cmake/exports.cmake

diff --git a/build/cmake/exports.cmake b/build/cmake/exports.cmake
index 4f9d043..3fcdd0c 100644
--- a/build/cmake/exports.cmake
+++ b/build/cmake/exports.cmake
@@ -27,23 +27,25 @@
 
   set(aom_sym_file "${AOM_CONFIG_DIR}/libaom.${symbol_file_ext}")
 
-  add_custom_target(generate_exports
-                    COMMAND ${CMAKE_COMMAND}
-                            -DAOM_ROOT="${AOM_ROOT}"
-                            -DAOM_CONFIG_DIR="${AOM_CONFIG_DIR}"
-                            -DAOM_TARGET_SYSTEM=${AOM_TARGET_SYSTEM}
-                            -DAOM_SYM_FILE="${aom_sym_file}"
-                            -DAOM_MSVC=${MSVC}
-                            -DAOM_XCODE=${XCODE}
-                            -DCONFIG_NAME=$<CONFIG>
-                            -DCONFIG_AV1_DECODER=${CONFIG_AV1_DECODER}
-                            -DCONFIG_AV1_ENCODER=${CONFIG_AV1_ENCODER}
-                            -DCONFIG_INSPECTION=${CONFIG_INSPECTION}
-                            -DENABLE_TESTS=${ENABLE_TESTS}
-                            -P
-                            "${AOM_ROOT}/build/cmake/generate_exports.cmake"
-                    SOURCES ${AOM_EXPORTS_SOURCES}
-                    DEPENDS ${AOM_EXPORTS_SOURCES} BYPRODUCTS ${aom_sym_file})
+  add_custom_target(
+    generate_exports
+    COMMAND ${CMAKE_COMMAND}
+            -DAOM_ROOT="${AOM_ROOT}"
+            -DAOM_CONFIG_DIR="${AOM_CONFIG_DIR}"
+            -DAOM_TARGET_SYSTEM=${AOM_TARGET_SYSTEM}
+            -DAOM_SYM_FILE="${aom_sym_file}"
+            -DAOM_MSVC=${MSVC}
+            -DAOM_XCODE=${XCODE}
+            -DCMAKE_SHARED_LIBRARY_PREFIX="${CMAKE_SHARED_LIBRARY_PREFIX}"
+            -DCONFIG_NAME=$<CONFIG>
+            -DCONFIG_AV1_DECODER=${CONFIG_AV1_DECODER}
+            -DCONFIG_AV1_ENCODER=${CONFIG_AV1_ENCODER}
+            -DCONFIG_INSPECTION=${CONFIG_INSPECTION}
+            -DENABLE_TESTS=${ENABLE_TESTS}
+            -P
+            "${AOM_ROOT}/build/cmake/generate_exports.cmake"
+    SOURCES ${AOM_EXPORTS_SOURCES}
+    DEPENDS ${AOM_EXPORTS_SOURCES} BYPRODUCTS ${aom_sym_file})
 
   # Make libaom depend on the exports file, and set flags to pick it up when
   # creating the dylib.

build/cmake/generate_exports.cmake

diff --git a/build/cmake/generate_exports.cmake b/build/cmake/generate_exports.cmake
index 8720ac8..3a5f67c 100644
--- a/build/cmake/generate_exports.cmake
+++ b/build/cmake/generate_exports.cmake
@@ -10,6 +10,7 @@
 #
 cmake_minimum_required(VERSION 3.5)
 
+# CMAKE_SHARED_LIBRARY_PREFIX can be empty
 set(REQUIRED_ARGS "AOM_ROOT" "AOM_CONFIG_DIR" "AOM_TARGET_SYSTEM" "AOM_SYM_FILE"
                   "CONFIG_AV1_DECODER" "CONFIG_AV1_ENCODER")
 
@@ -24,7 +25,8 @@
 if("${AOM_TARGET_SYSTEM}" STREQUAL "Darwin")
   set(symbol_prefix "_")
 elseif("${AOM_TARGET_SYSTEM}" MATCHES "Windows\|MSYS")
-  file(WRITE "${AOM_SYM_FILE}" "LIBRARY aom\n" "EXPORTS\n")
+  file(WRITE "${AOM_SYM_FILE}" "LIBRARY ${CMAKE_SHARED_LIBRARY_PREFIX}aom\n"
+                               "EXPORTS\n")
 else()
   set(symbol_suffix ";")
 endif()
@@ -34,7 +36,8 @@
 if("${AOM_TARGET_SYSTEM}" STREQUAL "Darwin")
   file(REMOVE "${aom_sym_file}")
 elseif("${AOM_TARGET_SYSTEM}" MATCHES "Windows\|MSYS")
-  file(WRITE "${aom_sym_file}" "LIBRARY aom\n" "EXPORTS\n")
+  file(WRITE "${aom_sym_file}" "LIBRARY ${CMAKE_SHARED_LIBRARY_PREFIX}aom\n"
+                               "EXPORTS\n")
 else()
   file(WRITE "${aom_sym_file}" "{\nglobal:\n")
 endif()