Bug 1434601

Description of problem:
when you try use gdb inside of emacs the mode doesn't initialize and then it becomes nearly unusable because you're left interacting with the machine interface.

Version-Release number of selected component (if applicable):
emacs-filesystem-25.2-0.1.rc2.fc26.noarch
emacs-common-25.2-0.1.rc2.fc26.x86_64
emacs-nox-25.2-0.1.rc2.fc26.x86_64


How reproducible:
always

Steps to Reproduce:
1. inside of emacs do M-x gdb
2. it will fill in a command line like: 
Run gdb (like this): gdb -i=mi /omp-test1
hit enter
3. instead of giving you a nice UI it will print something like:
Current directory is /
Error: you did not specify -i=mi on GDB's command line!
Python runtime initialized with LC_CTYPE=C (a locale with default ASCII encoding), which may cause Unicode compatibility problems. Using \
C.UTF-8, C.utf8, or UTF-8 (if available) as alternative Unicode-compatible locales is recommended.
=thread-group-added,id="i1"
~"GNU gdb (GDB) Fedora 7.12.50.20170309-5.fc27\n"
~"Copyright (C) 2017 Free Software Foundation, Inc.\n"
~"License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>\nThis is free software: you are free to change and redist\
ribute it.\nThere is NO WARRANTY, to the extent permitted by law.  Type \"show copying\"\nand \"show warranty\" for details.\n"
~"This GDB was configured as \"x86_64-redhat-linux-gnu\".\nType \"show configuration\" for configuration details."
~"\nFor bug reporting instructions, please see:\n"
~"<http://www.gnu.org/software/gdb/bugs/>.\n"
~"Find the GDB manual and other documentation resources online at:\n<http://www.gnu.org/software/gdb/documentation/>.\n"
~"For help, type \"help\".\n"
~"Type \"apropos word\" to search for commands related to \"word\"...\n"
~"Reading symbols from /omp-test1..."
~"done.\n"
(gdb)
1^done
(gdb)
2^done
(gdb)
3^done
(gdb)
4^done
(gdb)
5^done,files=[{file="openmp.cc",fullname="/openmp.cc"},{file="/usr/include/c++/7/cstdlib",fullname="/usr/include/c++/7/cstdlib"},{file="/\
usr/include/c++/7/cmath",fullname="/usr/include/c++/7/cmath"},{file="/usr/include/c++/7/x86_64-redhat-linux/bits/c++config.h",fullname="/\
usr/include/c++/7/x86_64-redhat-linux/bits/c++config.h"},{file="/usr/lib/gcc/x86_64-redhat-linux/7/include/stddef.h",fullname="/usr/lib/g\
cc/x86_64-redhat-linux/7/include/stddef.h"},{file="/usr/include/stdlib.h",fullname="/usr/include/stdlib.h"},{file="/usr/include/math.h",f\
ullname="/usr/include/math.h"},{file="<built-in>",fullname="//<built-in>"}]
(gdb)
6^done,line="1",file="openmp.cc",fullname="/openmp.cc",macro-info="0"
(gdb)
7^done,value="(gdb) "
(gdb)
8^error,msg="No registers."
(gdb)
9^done,threads=[]
(gdb)
10^done,BreakpointTable={nr_rows="0",nr_cols="6",hdr=[{width="7",alignment="-1",col_name="number",colhdr="Num"},{width="14",alignment="-1\
",col_name="type",colhdr="Type"},{width="4",alignment="-1",col_name="disp",colhdr="Disp"},{width="3",alignment="-1",col_name="enabled",co\
lhdr="Enb"},{width="10",alignment="-1",col_name="addr",colhdr="Address"},{width="40",alignment="2",col_name="what",colhdr="What"}],body=[\
]}
(gdb)
11^done,threads=[]
(gdb)
12^done,BreakpointTable={nr_rows="0",nr_cols="6",hdr=[{width="7",alignment="-1",col_name="number",colhdr="Num"},{width="14",alignment="-1\
",col_name="type",colhdr="Type"},{width="4",alignment="-1",col_name="disp",colhdr="Disp"},{width="3",alignment="-1",col_name="enabled",co\
lhdr="Enb"},{width="10",alignment="-1",col_name="addr",colhdr="Address"},{width="40",alignment="2",col_name="what",colhdr="What"}],body=[\
]}


Additional info:

It looks to me like something is going wrong in:
(defun gdb--check-interpreter (filter proc string)
  (unless (zerop (length string))
    (remove-function (process-filter proc) #'gdb--check-interpreter)
    (unless (memq (aref string 0) '(?^ ?~ ?@ ?& ?* ?=))
      ;; Apparently we're not running with -i=mi.                                                                                         
      (let ((msg "Error: you did not specify -i=mi on GDB's command line!"))
        (message msg)
        (setq string (concat (propertize msg 'font-lock-face 'error)
                             "\n" string)))
      ;; Use the old gud-gbd filter, not because it works, but because it                                                                 
      ;; will properly display GDB's answers rather than hanging waiting for                                                              
      ;; answers that aren't coming.                                                                                                      
      (set (make-local-variable 'gud-marker-filter) #'gud-gdb-marker-filter))
    (funcall filter proc string)))

I think that the problem is when you run emacs in a minimal container the first thing that it prints out is:

[root@1eadb6a256ad /]# gdb -i=mi omp_test1
Python runtime initialized with LC_CTYPE=C (a locale with default ASCII encoding), which may cause Unicode compatibility problems. Using C.UTF-8, C.utf8, or UTF-8 (if available) as alternative Unicode-compatible locales is recommended.
=thread-group-added,id="i1"
~"GNU gdb (GDB) Fedora 7.12.50.20170309-5.fc27\n"

and that python warning before the GDB banner confuses the gdb-mi mode.