configure.ac: generate prte_version.h properly

Have prte_version.h generated via AC_CONFIG_HEADERS, not
AC_CONFIG_FILES.  This properly quotes strings (which technically
doesn't matter here since prte_version.h doesn't include any strings)
and also won't overwrite the resulting .h file if it hasn't changed.

NOTE: This is a fix for the original commit that brought in this
functionality (4da431a) which broke in at least some Linux
environments.  Apparently, AC_CONFIG_HEADERS -- unlike AC_CONFIG_FILES
-- does not like extra newlines at the beginning or end of the file
list parameter in at least some Linux environments (although it seems
to work find on macOS).  Shrug!

Signed-off-by: Jeff Squyres <[email protected]>
(cherry picked from commit b7196af)

configure.ac

@@ -205,7 +205,8 @@ AC_MSG_RESULT([$ltversion])
 
 # List header files to generate
 
-AC_CONFIG_HEADERS([src/include/prte_config.h])
+AC_CONFIG_HEADERS([src/include/prte_config.h
+                   include/prte_version.h])
 
 prte_show_subtitle "Initialization, setup"
 
@@ -1016,7 +1017,6 @@ AC_CONFIG_FILES([
     config/Makefile
     contrib/Makefile
     include/Makefile
-    include/prte_version.h
     docs/Makefile
     src/docs/Makefile
     src/docs/prrte-rst-content/Makefile