configure script fails to detect "float word ordering" on Solaris

[wiggin15]

BPO	38527
Nosy	@jcea, @wiggin15, @miss-islington, @isidentical
PRs	bpo-38527: fix configure script for Solaris #16845 [3.8] bpo-38527: fix configure script for Solaris (GH-16845) #19279

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2020-04-01.16:52:39.219>
created_at = <Date 2019-10-19.14:47:05.851>
labels = ['build', '3.8', '3.9']
title = 'configure script fails to detect "float word ordering" on Solaris'
updated_at = <Date 2020-04-01.16:52:39.219>
user = 'https://github.com/wiggin15'

bugs.python.org fields:

activity = <Date 2020-04-01.16:52:39.219>
actor = 'pablogsal'
assignee = 'none'
closed = True
closed_date = <Date 2020-04-01.16:52:39.219>
closer = 'pablogsal'
components = ['Build']
creation = <Date 2019-10-19.14:47:05.851>
creator = 'wiggin15'
dependencies = []
files = []
hgrepos = []
issue_num = 38527
keywords = ['patch']
message_count = 3.0
messages = ['354941', '365485', '365487']
nosy_count = 4.0
nosy_names = ['jcea', 'wiggin15', 'miss-islington', 'BTaskaya']
pr_nums = ['16845', '19279']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue38527'
versions = ['Python 3.8', 'Python 3.9']

[wiggin15]

When running the configure script on Solaris SPARC (versions 10 and 11), the script fails with the following error:

checking whether float word ordering is bigendian... unknown
configure: error:

Unknown float word ordering. You need to manually preset
ax_cv_c_float_words_bigendian=no (or yes) according to your system.

The configure script uses "grep" on a compiled binary to see how a float variable is compiled. On Solaris, the regular "grep" command may be an old version that fails to search in a binary file. The correct command should be "ggrep" (the GNU grep).
Luckily, Python's configure script already finds this command in an earlier check:

checking for grep that handles long lines and -e... /usr/bin/ggrep

All we have to do, then, is use the command that configure finds. i.e. replace "grep" -> "$GREP".

[miss-islington]

New changeset 5dd8360 by Arnon Yaari in branch 'master':
bpo-38527: fix configure script for Solaris (GH-16845)
5dd8360

[miss-islington]

New changeset fc03640 by Miss Islington (bot) in branch '3.8':
bpo-38527: fix configure script for Solaris (GH-16845)
fc03640