USE_PKGSRC_GCC and circular dependency

[Zhiwen Zheng <zhiwen%40701.xyz@localhost>]

Should I use "USE_PKGSRC_GCC=no" to build gcc7 and its deps, and switch to "USE_PKGSRC_GCC=yes" after install of gcc7?
Will "USE_PKGSRC_GCC_RUNTIME = yes" take effect when "USE_PKGSRC_GCC=no", i.e. the newly created gcc7 use the newly created gcc7-libs or
use the parent gcc runtime ?

=======mk.conf==============
# Example /opt/local/etc/mk.conf file produced by bootstrap-pkgsrc
# Thu Mar 12 10:47:10 CST 2020

.ifdef BSD_PKG_MK	# begin pkgsrc settings

ABI=			32
PKGSRC_COMPILER=	gcc

PKG_DBDIR=		/opt/local/pkgdb
LOCALBASE=		/opt/local
VARBASE=		/opt/local/var
PKG_TOOLS_BIN=		/opt/local/sbin
PKGINFODIR=		info
PKGMANDIR=		man

TOOLS_PLATFORM.install?=	/opt/local/bin/bsdinstall
TOOLS_PLATFORM.awk?=		/opt/local/bin/nawk
TOOLS_PLATFORM.sed?=		/opt/local/bin/nbsed
TOOLS_PLATFORM.sh?=		/usr/bin/bash

.endif			# end pkgsrc settings
DISTDIR=			/opt/distfiles
WRKOBJDIR=			/opt/work
PACKAGES=			/opt/packages

GCC_REQD=			7.4
USE_PKGSRC_GCC=			yes
USE_PKGSRC_GCC_RUNTIME= 	yes

ACCEPTABLE_LICENSES+= 	oracle-binary-code-license

=======================================
-bash-4.3# cd devel/git
-bash-4.3# bmake package
===> Skipping vulnerability checks.
WARNING: No /opt/local/pkgdb/pkg-vulnerabilities file found.
WARNING: To fix run: `/opt/local/sbin/pkg_admin -K /opt/local/pkgdb fetch-pkg-vulnerabilities'.
===> Installing dependencies for git-2.24.1
=> Build dependency cwrappers>=20150314: found cwrappers-20180325
=> Full dependency git-base>=2.24.1: NOT found
=> Verifying package-install for ../../devel/git-base
=> Bootstrap dependency digest>=20010302: NOT found
=> Verifying package-install for ../../pkgtools/digest
===> Skipping vulnerability checks.
WARNING: No /opt/local/pkgdb/pkg-vulnerabilities file found.
WARNING: To fix run: `/opt/local/sbin/pkg_admin -K /opt/local/pkgdb fetch-pkg-vulnerabilities'.
===> Installing dependencies for digest-20190127
=> Build dependency gcc7>=7.4: NOT found
=> Verifying package-install for ../../lang/gcc7
=> Bootstrap dependency digest>=20010302: NOT found
=> Verifying package-install for ../../pkgtools/digest
ERROR: This package has set PKG_FAIL_REASON:
ERROR: Circular dependency detected
*** Error code 255

Stop.
bmake[4]: stopped in /opt/pkgsrc/pkgtools/digest
*** Error code 1

Stop.
bmake[3]: stopped in /opt/pkgsrc/lang/gcc7
*** Error code 1

Stop.
bmake[2]: stopped in /opt/pkgsrc/pkgtools/digest
*** Error code 1

Stop.
bmake[1]: stopped in /opt/pkgsrc/devel/git-base
*** Error code 1

Stop.
bmake: stopped in /opt/pkgsrc/devel/git