MDEV-5620 CMake option to compile against an external PCRE library

cmake/jemalloc.cmake

@@ -46,7 +46,7 @@ ELSE()
 ENDIF()
 
 SET(WITH_JEMALLOC ${WITH_JEMALLOC_DEFAULT} CACHE STRING
-    "Which jemalloc to use (possible values are 'no', 'bundled', 'system', 'yes' (system if possible, otherwise bundled)")
+    "Which jemalloc to use. Possible values are 'no', 'bundled', 'system', 'yes' (system if possible, otherwise bundled)")
 
 MACRO (CHECK_JEMALLOC)
   IF(WITH_JEMALLOC STREQUAL "system" OR WITH_JEMALLOC STREQUAL "yes")

cmake/pcre.cmake

@@ -0,0 +1,16 @@
+SET(WITH_PCRE "auto" CACHE STRING
+   "Which pcre to use (possible values are 'bundled', 'system', or 'auto')")
+
+MACRO (CHECK_PCRE)
+  IF(WITH_PCRE STREQUAL "system" OR WITH_PCRE STREQUAL "auto")
+    CHECK_LIBRARY_EXISTS(pcre pcre_stack_guard "" HAVE_PCRE)
+  ENDIF()
+  IF(NOT HAVE_PCRE)
+    IF (WITH_PCRE STREQUAL "system")
+      MESSAGE(FATAL_ERROR "system pcre is not found or unusable")
+    ENDIF()
+    SET(PCRE_INCLUDES ${CMAKE_BINARY_DIR}/pcre ${CMAKE_SOURCE_DIR}/pcre)
+    ADD_SUBDIRECTORY(pcre)
+  ENDIF()
+ENDMACRO()
+

cmake/plugin.cmake

@@ -37,8 +37,7 @@ MACRO(MYSQL_ADD_PLUGIN)
   # Add common include directories
   INCLUDE_DIRECTORIES(${CMAKE_SOURCE_DIR}/include 
                     ${CMAKE_SOURCE_DIR}/sql
-                    ${CMAKE_BINARY_DIR}/pcre
-                    ${CMAKE_SOURCE_DIR}/pcre
+                    ${PCRE_INCLUDES}
                     ${SSL_INCLUDE_DIRS}
                     ${ZLIB_INCLUDE_DIR})