Merge pull request #161 from annlew/noresm2_1_dev_chempp_bug

Increase the char length for path to compiler in chem_pp code

Contributors: @annlew, @sarambl
Reviewers: @gold2718
Purpose of changes: Avoid chemistry preprocessor failure at compilation when path to 
                                    compiler exceeds 64 characters

Github PR URL: #161

Changes made to build system: Only chemistry preprocessor when usr_mech_infile
                                                 is specified in env_build.xml 
Changes made to the namelist: None
Changes to the defaults for the boundary datasets: None
Substantial timing or memory changes: None
Change the char length for cpp path from 64 to 256 in chem_pp code. 

Test: SMS allactive test with grid = f19_tn14 and compset=NF2000climo with a testmod to run the chemistry preprocessor. Fails with current HEAD of noresm2_1_develop, passes with this PR branch.

Issues addressed by this PR: 
cam_chempp issue with usr_mech_infile when path to compiler is too long (#160)

chem_proc/src/cam_chempp/mozpp.main.f

@@ -71,7 +71,7 @@ program mozart_pp
       character(len=580) :: command, cpp_command
       character(len=256) :: errcom, filout, filin
       character(len=64)  :: oper_flpth
-      character(len=64)  :: cpp_dir, cpp_opts
+      character(len=256)  :: cpp_dir, cpp_opts
       character(len=64)  :: wrk_dir
       character(len=64)  :: tar_flnm
       character(len=64)  :: subfile