docs: replace `FOO by :term:FOO` where possible

If a variable has a glossary entry and some rST files write about those
variables, it's better to point to the glossary entry instead of just
highlighting it by surrounding it with two tick quotes.

This was automated by the following python script:
"""
import re
from pathlib import Path

with open('objects.inv.txt', 'r') as f:
    objects = f.readlines()

with open('bitbake-objects.inv.txt', 'r') as f:
    objects = objects + f.readlines()

re_term = re.compile(r'variables.html#term-([A-Z_0-9]*)')
terms = []

for obj in objects:
    match = re_term.search(obj)
    if match and match.group(1):
        terms.append(match.group(1))

for rst in Path('.').rglob('*.rst'):
    with open(rst, 'r') as f:
        content = "".joing(f.readlines())
    for term in terms:
        content = re.sub(r'``({})``(?!.*\s*[~-]+)'.format(term), r':term:`\1`', content)

    with open(rst, 'w') as f:
        f.write(content)
"""

(From yocto-docs rev: ba49d9babfcb84bc5c26a68c8c3880a1d9c236d3)

Signed-off-by: Quentin Schulz <foss@0leil.net>
Reviewed-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Reviewed-by: Nicolas Dechesne <nicolas.dechesne@linaro.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/migration-guides/migration-2.0.rst

@@ -25,7 +25,7 @@ and the porting guide at
 https://gcc.gnu.org/gcc-5/porting_to.html.
 
 Alternatively, you can switch back to GCC 4.9 or 4.8 by setting
-``GCCVERSION`` in your configuration, as follows::
+:term:`GCCVERSION` in your configuration, as follows::
 
    GCCVERSION = "4.9%"
 
@@ -244,7 +244,7 @@ The following QA checks have been added:
 
 -  Added an "invalid-packageconfig" check for any options specified in
    :term:`PACKAGECONFIG` that do not match any
-   ``PACKAGECONFIG`` option defined for the recipe.
+   :term:`PACKAGECONFIG` option defined for the recipe.
 
 .. _migration-2.0-miscellaneous: