Fix javah for strict javah & ordering.

* javah on some JDKs is strict about sourcing, and no classpath entry
  referencing the jar was present for the javah command, either as an argument
  or in the environment.
* javah was chained as a post-build of the jar creation. This caused breakage
  if src/java/*.cc tried to use the javah-generated .h file before it was
  generated.

Fixes: https://tickets.puppetlabs.com/browse/FACT-1541
Fixes: https://bugs.gentoo.org/show_bug.cgi?id=600942
Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>

diff -Nuar facter-9999.orig/lib/CMakeLists.txt facter-9999/lib/CMakeLists.txt
--- facter-9999.orig/lib/CMakeLists.txt	2016-11-28 22:18:29.366271544 -0800
+++ facter-9999/lib/CMakeLists.txt	2016-11-28 22:28:36.244894899 -0800
@@ -267,7 +267,15 @@
     include(UseJava)
-    add_jar(facter-jruby "${CMAKE_BINARY_DIR}/lib/com/puppetlabs/Facter.java" OUTPUT_NAME facter OUTPUT_DIR "${CMAKE_BINARY_DIR}/lib" ENTRY_POINT com/puppetlabs/Facter)
+    add_jar(facter-jruby-jar "${CMAKE_BINARY_DIR}/lib/com/puppetlabs/Facter.java" OUTPUT_NAME facter OUTPUT_DIR "${CMAKE_BINARY_DIR}/lib" ENTRY_POINT com/puppetlabs/Facter)
 
-    add_custom_command(TARGET facter-jruby POST_BUILD COMMAND javah ARGS -d "${CMAKE_CURRENT_LIST_DIR}/src/java" com.puppetlabs.Facter WORKING_DIRECTORY "${CMAKE_BINARY_DIR}/lib")
+    # javah does not atomically write the header file, so parallel builds can
+    # read it before it finishes writing if not careful.
+    add_custom_command(OUTPUT "${CMAKE_CURRENT_LIST_DIR}/src/java/com_puppetlabs_Facter.h"
+                       COMMAND javah ARGS -classpath facter.jar -d "${CMAKE_CURRENT_LIST_DIR}/src/java" com.puppetlabs.Facter
+                       WORKING_DIRECTORY "${CMAKE_BINARY_DIR}/lib"
+                       DEPENDS facter-jruby-jar)
+    # Anything that depends on facter-jruby wants both the jar AND the completely written header.
+    add_custom_target(facter-jruby DEPENDS facter-jruby-jar "${CMAKE_CURRENT_LIST_DIR}/src/java/com_puppetlabs_Facter.h")
+    set(LIBFACTER_COMMON_SOURCES ${LIBFACTER_COMMON_SOURCES} src/java/com_puppetlabs_Facter.h)
 endif()
 
 # Set include directories