Don't use temporary file when creating tag files without running preprocessor

Don't use temporary file when creating tag files without running preprocessor

The tm_workspace_create_global_tags() function generates tags for
two cases:

1. Source files pre-processed by C pre-processor. It first generates
a file combining the parsed header files by creating a temporary
file in which all the header files are included and this file is passed
to the pre-processor. The result of the pre-processed file is then
parsed by the ctags parser.
2. Source files directly parsed by the ctags parser. In this case all
the source files are concatenated to a single file which is then parsed
by the ctags parser.

This patch leaves (1) more or less unchanged; however, the creation of
the temporary file in (2) is unnecessary - the individual files can
be parsed directly, the tags from all the parses can be combined, sorted
and pruned without creating the temporary file.

The temporary file is a problem for unit tests where some languages
use the file name as the name of module in which the tags are defined
and by using a different name, the unit test generates a different tag
file every time it's run.

Note the changed output of the process_order unit test caused by this
change. The test parses two files, one containing

enum {
	I1_E1,
	I1_E2,
};

the other contining

enum {
	I2_E1,
	I2_E2,
};

Previously, because the files were concatenated the enums were different
tags and the anonnymous tag renaming function renamed them to anon_enum_1
and anon_enum_2. Because now the files are parsed separately, the
enum from the first file gets renamed to anon_enum_1 and when parsing
the second file, we get the name anon_enum_1 as well for the second enum.
This however isn't a problem - we don't display global tags in the
symbol tree, autocompletion, and they are also ignored in scope completion
so this shouldn't matter much.