Experimental Physics and
Industrial Control System

Yes, it does look like a problem with building epics base on MacOS (at least with 10.14) with Apple-supplied Perl (5.18).   I get the same error as you (perl's XS tool cannot find its EXTERN.h) trying to build both base-3.16.2 and base-7.0.2 with Apple-supplied Perl (/usr/bin/perl).

I can build both base-3-16.2 and base-7.0.2 using perl (5.26) from MacPorts.  Using that perl  which got installed to /opt/local/bin/perl), the section of the build looks like this:

/Applications/Xcode.app/Contents/Developer/usr/bin/make -C O.darwin-x86 -f ../Makefile TOP=../../.. \

    T_A=darwin-x86 install

rm -f Cap5.c Cap5.c_new

perl -CSD /opt/local/bin/xsubpp -typemap /opt/local/lib/perl5/5.26/ExtUtils/typemap ../Cap5.xs > Cap5.c_new && mv Cap5.c_new Cap5.c

perl -CSD /Users/Newville/local/epics/base-7.0.2/bin/darwin-x86/mkmf.pl  -m Cap5.d -I. -I../O.Common -I. -I. -I.. -I/Users/Newville/local/epics/base-7.0.2/include/compiler/clang -I/Users/Newville/local/epics/base-7.0.2/include/os/Darwin -I/Users/Newville/local/epics/base-7.0.2/include -I/Users/Newville/local/epics/base-7.0.2/include/compiler/clang -I/Users/Newville/local/epics/base-7.0.2/include/os/Darwin -I/Users/Newville/local/epics/base-7.0.2/include   -I/opt/local/lib/perl5/5.26/darwin-thread-multi-2level/CORE     Cap5.o Cap5.c

cc              -DUNIX  -Ddarwin     -O3 -g   -Wall   -fno-common -DPERL_DARWIN -mmacosx-version-min=10.13 -pipe -Os  -fno-strict-aliasing -fstack-protector-strong -I/opt/local/include -DPERL_USE_SAFE_PUTENV    -arch x86_64    -fno-common -fPIC -I. -I../O.Common -I. -I. -I.. -I/Users/Newville/local/epics/base-7.0.2/include/compiler/clang -I/Users/Newville/local/epics/base-7.0.2/include/os/Darwin -I/Users/Newville/local/epics/base-7.0.2/include -I/Users/Newville/local/epics/base-7.0.2/include/compiler/clang -I/Users/Newville/local/epics/base-7.0.2/include/os/Darwin -I/Users/Newville/local/epics/base-7.0.2/include   -I/opt/local/lib/perl5/5.26/darwin-thread-multi-2level/CORE     -c Cap5.c

c++ -o Cap5.bundle -bundle -undefined dynamic_lookup -L/Users/Newville/local/epics/base-7.0.2/lib/darwin-x86        -arch x86_64            Cap5.o    -lca -lCom      -lreadline -lm 

Installing loadable shared library /Users/Newville/local/epics/base-7.0.2/lib/perl/5.26.2/darwin-thread-multi-2level/Cap5.bundle

which does correctly specifiy the include path for EXTERN.h as /opt/local/lib/perl5/5.26/darwin-thread-multi-2level/CORE.

It seems like "/usr/bin/perl -V" is not reporting the absolute location of its include directories correctly, which might be part of the problem:

~> /usr/bin/perl -V

....

 @INC:

    /Library/Perl/5.18/darwin-thread-multi-2level

    /Library/Perl/5.18

    /Network/Library/Perl/5.18/darwin-thread-multi-2level

    /Network/Library/Perl/5.18

    /Library/Perl/Updates/5.18.2/darwin-thread-multi-2level

    /Library/Perl/Updates/5.18.2

    /System/Library/Perl/5.18/darwin-thread-multi-2level

    /System/Library/Perl/5.18

    /System/Library/Perl/Extras/5.18/darwin-thread-multi-2level

    /System/Library/Perl/Extras/5.18

    .

whereas EXTERN.h is actually in /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Perl/5.18/darwin-thread-multi-2level/CORE/EXTERN.h

Hope that helps.

--Matt