R @4.0.2: configure hangs under trace mode

[chrstphrchvz (Christopher Chavez)]

I observe that on macOS 10.15, running port -vst configure R hangs indefinitely (0% CPU usage) after these steps:

checking whether the ccache /usr/bin/clang++ linker (/Library/Developer/CommandLineTools/usr/bin/ld) supports shared libraries... yes
checking dynamic linker characteristics... darwin19.6.0 dyld
checking how to hardcode library paths into programs... immediate

Without trace mode, it proceeds immediately:

checking whether the ccache /usr/bin/clang++ linker (/Library/Developer/CommandLineTools/usr/bin/ld) supports shared libraries... yes
checking dynamic linker characteristics... darwin19.6.0 dyld
checking how to hardcode library paths into programs... immediate
checking if libtool supports shared libraries... yes
checking whether to build shared libraries... yes
checking whether to build static libraries... no
checking for /opt/local/bin/gfortran-mp-10 option to produce PIC... -fno-common

[chrstphrchvz (Christopher Chavez)]

Disabling ccache made no difference.

The configure script is hanging at line 19590:

eval "$ac_link" 2>&1 >/dev/null | $SED '/^$/d; /^ *+/d' >conftest.err

Setting configure.cmd sh -vx ./configure, and inserting echo 19590 at line 19590, the few lines of output before it gets stuck:

  fi # test -n "$compiler"

  GCC=$lt_save_GCC
  CC=$lt_save_CC
  CFLAGS=$lt_save_CFLAGS
fi # test yes != "$_lt_disable_FC"
+ test yes '!=' ''
+ lt_simple_compile_test_code='      subroutine t
      return
      end
'
+ lt_simple_link_test_code='      program t
      end
'
+ LTCC=/usr/bin/clang
+ LTCFLAGS='-pipe -Os -isysroot/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk -arch x86_64'
+ compiler=/usr/bin/clang
+ ac_outfile=conftest.o
+ echo '      subroutine t
      return
      end
'
+ eval '$FC -c $FCFLAGS $ac_fcflags_srcext conftest.$ac_ext >&5'
+ /usr/bin/sed '/^$/d; /^ *+/d'
cat conftest.err
++ cat conftest.err
+ _lt_compiler_boilerplate='$FC -c $FCFLAGS $ac_fcflags_srcext conftest.$ac_ext >&5'
+ rm -f conftest.a conftest.b conftest.err conftest.f conftest.o
+ ac_outfile=conftest.o
+ echo '      program t
      end
'
+ echo 19590
19590
+ eval '$FC -o conftest$ac_exeext $FCFLAGS $LDFLAGS $ac_fcflags_srcext conftest.$ac_ext $LIBS >&5'
+ /usr/bin/sed '/^$/d; /^ *+/d'

[chrstphrchvz (Christopher Chavez)]

Possibly related to #61233