fix RHEL8 "ambiguous python shebang" build failures

CMakeLists.txt

@@ -330,6 +330,7 @@ MYSQL_CHECK_SSL()
 MYSQL_CHECK_READLINE()
 
 SET(MALLOC_LIBRARY "system")
+SET(PYTHON_SHEBANG "/usr/bin/env python")
 
 CHECK_PCRE()
 

cmake/cpack_rpm.cmake

@@ -219,6 +219,8 @@ ELSEIF(RPM MATCHES "fedora" OR RPM MATCHES "(rhel|centos)7")
   ALTERNATIVE_NAME("server" "mariadb-server")
   ALTERNATIVE_NAME("server" "mysql-compat-server")
   ALTERNATIVE_NAME("test"   "mariadb-test")
+ELSEIF(RPM MATCHES "(rhel|centos)8")
+  SET(PYTHON_SHEBANG "/usr/bin/python3")
 ENDIF()
 
 # workaround for lots of perl dependencies added by rpmbuild

storage/rocksdb/CMakeLists.txt

@@ -217,7 +217,9 @@ TARGET_LINK_LIBRARIES(sst_dump rocksdblib)
 MYSQL_ADD_EXECUTABLE(mysql_ldb tools/mysql_ldb.cc COMPONENT rocksdb-engine)
 TARGET_LINK_LIBRARIES(mysql_ldb rocksdb_tools rocksdb_aux_lib)
 
-INSTALL_SCRIPT(myrocks_hotbackup COMPONENT rocksdb-engine)
+CONFIGURE_FILE(${CMAKE_CURRENT_SOURCE_DIR}/myrocks_hotbackup.py
+  ${CMAKE_CURRENT_BINARY_DIR}/myrocks_hotbackup @ONLY)
+INSTALL_SCRIPT(${CMAKE_CURRENT_BINARY_DIR}/myrocks_hotbackup COMPONENT rocksdb-engine)
 
 IF(CMAKE_CXX_COMPILER_ID MATCHES "GNU" OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
   SET_TARGET_PROPERTIES(rocksdb_tools sst_dump mysql_ldb PROPERTIES COMPILE_FLAGS -frtti)

storage/rocksdb/myrocks_hotbackup → storage/rocksdb/myrocks_hotbackup.py

-#!/usr/bin/env python
+#!@PYTHON_SHEBANG@
 
 from __future__ import division
 from optparse import OptionParser