Description of problem:

Builds fail with:
2. Task: 478271-master, importing the package: None
Build via Mock
/usr/bin/mock -r epel-7-x86_64 --uniqueext 478271-master --scm-enable --scm-option method=git --scm-option package=glibc --scm-option branch= --scm-option write_tar=True --scm-option spec=glibc.spec --scm-option git_get=git clone --depth 1 git://pkgs.fedoraproject.org/rpms/glibc.git glibc --buildsrpm --resultdir=/tmp/tmpWfiyrC
Exception raised during srpm import:
Traceback (most recent call last):
  File "/usr/share/copr/dist_git/dist_git_importer.py", line 526, in do_import
    provider.get_srpm()
  File "/usr/share/copr/dist_git/dist_git_importer.py", line 170, in get_srpm
    self.provider.get_srpm()
  File "/usr/share/copr/dist_git/dist_git_importer.py", line 321, in get_srpm
    raise SrpmBuilderException(error)
SrpmBuilderException: INFO: mock.py version 1.2.21 starting (python version = 3.4.3)...
Start: init plugins
INFO: selinux enabled
Finish: init plugins
Start: run
cat: /builddir/build/SOURCES/SUPPORTED: No such file or directory
cat: /builddir/build/SOURCES/SUPPORTED: No such file or directory
INFO: Start(/tmp/tmpctz2os43.mock-scm.glibc/glibc/glibc.spec)  Config(epel-7-x86_64)
Start: clean chroot
Finish: clean chroot
Start: chroot init
INFO: calling preinit hooks
INFO: enabled root cache
Start: unpacking root cache
Finish: unpacking root cache
INFO: enabled yum cache
Start: cleaning yum metadata
Finish: cleaning yum metadata
Mock Version: 1.2.21
INFO: Mock Version: 1.2.21
Start: yum update
Finish: yum update
Finish: chroot init
Start: buildsrpm
Start: rpmbuild -bs
Finish: rpmbuild -bs
Finish: buildsrpm
ERROR: Exception(/tmp/tmpctz2os43.mock-scm.glibc/glibc/glibc.spec) Config(epel-7-x86_64) 0 minutes 47 seconds
INFO: Results and/or logs in: /tmp/tmpWfiyrC
INFO: Cleaning up build root ('cleanup_on_failure=True')
Start: clean chroot
Finish: clean chroot
ERROR: Command failed. See logs for output.
 # bash --login -c /usr/bin/rpmbuild -bs --target x86_64 --nodeps /builddir/build/SPECS/glibc.spec

Sending back: 
{"task_id": "478271-master", "error": "srpm_build_error"}


Version-Release number of selected component (if applicable):


How reproducible:
The issue reproduces repeatably.

Steps to Reproduce:

mock -r epel-7-x86_64 --scm-enable --scm-option method=git --scm-option branch= --scm-option write_tar=True --scm-option spec=glibc.spec --scm-option package=glibc --scm-option git_get="git clone --depth 1 git://pkgs.fedoraproject.org/rpms/glibc.git glibc" --buildsrpm

Actual results:
Mock Version: 1.2.21
ENTER ['do'](['bash', '--login', '-c', '/usr/bin/rpmbuild -bs --target x86_64 --nodeps /builddir/build/SPECS/glibc.spec'], user='mockbuild'env={'SHELL': '/bin/bash', 'HOSTNAME': 'mock', 'PATH': '/usr/bin:/bin:/usr/sbin:/sbin', 'PROMPT_COMMAND': 'printf "\\033]0;<mock-chroot>\\007"', 'HOME': '/builddir', 'TERM': 'vt100', 'LANG': 'en_US.utf8', 'PS1': '<mock-chroot> \\s-\\v\\$ '}gid=135timeout=0chrootPath='/home/carlos/scratch/mock/epel-7-x86_64/root'printOutput=Trueuid=1000shell=Falselogger=<mockbuild.trace_decorator.getLog object at 0x7f1d80e2eda0>)
Executing command: ['bash', '--login', '-c', '/usr/bin/rpmbuild -bs --target x86_64 --nodeps /builddir/build/SPECS/glibc.spec'] with env {'SHELL': '/bin/bash', 'HOSTNAME': 'mock', 'PATH': '/usr/bin:/bin:/usr/sbin:/sbin', 'PROMPT_COMMAND': 'printf "\\033]0;<mock-chroot>\\007"', 'HOME': '/builddir', 'TERM': 'vt100', 'LANG': 'en_US.utf8', 'PS1': '<mock-chroot> \\s-\\v\\$ '} and shell False
error: line 340: Unknown tag: Recommends: libcrypt-nss(x86-64)
Building target platforms: x86_64
Building for target x86_64
Child return code was: 1
EXCEPTION: [Error()]
Traceback (most recent call last):
  File "/usr/lib/python3.4/site-packages/mockbuild/trace_decorator.py", line 88, in trace
    result = func(*args, **kw)
  File "/usr/lib/python3.4/site-packages/mockbuild/util.py", line 562, in do
    raise exception.Error("Command failed. See logs for output.\n # %s" % (command,), child.returncode)
mockbuild.exception.Error: Command failed. See logs for output.
 # bash --login -c /usr/bin/rpmbuild -bs --target x86_64 --nodeps /builddir/build/SPECS/glibc.spec


Expected results:
glibc rawhide builds just fine.

Additional info:
An EPEL7 mock chroot can't be used to build an SRPM that could have features it doesn't know about.

Any reason why we don't use a rawhide mock chroot to build the SRPM?