Add build configuration checks

[Andrew Johnson]

Dirk Zimoch reported:

EPICS 7 could be more verbose in case of configuration errors.

If I try this:
make CROSS_COMPILER_TARGET_ARCHS=doesnotexist

I do not get an error message complaining about missing configuration files for the "doesnotexist" architecture.

Instead I get:
make[4]: Entering directory `/afs/psi.ch/group/8431/dirk/git/BASE/base-7.0.1-pre1/modules/libcom/src/O.doesnotexist'
perl -CSD ../../src/error/makeStatTbl.pl ../../src/osi/devLib.h ../../src/osi/epicsTime.h ../../src/as/asLib.h ../../src/misc/epicsStdlib.h ../../src/pool/epicsThreadPool.h ../../src/error/errMdef.h
perl -CSD ../../src/env/bldEnvData.pl -t doesnotexist \
        -c gcc -s /usr/local/epics/base-7.0.1/configure
Usage: bldEnvData.pl [options] configure
  -h Help: Print this message
  -q Quiet: Only print errors
  -o file Output filename, default is envData.c
  -t arch Target architecture $(T_A) name
  -s os Operating system $(OS_CLASS)
  -c comp Compiler class $(CMPLR_CLASS)

/usr/local/epics/base-7.0.1/bin/RHEL7-x86_64/e_flex -S/usr/local/epics/base-7.0.1/include/flex.skel.static -8 -I -t ../../src/as/asLib_lex.l > asLib_lex.yy.c
mv asLib_lex.yy.c asLib_lex.c
/usr/local/epics/base-7.0.1/bin/RHEL7-x86_64/antelope -basLib ../../src/as/asLib.y
mv asLib.tab.c asLib.c
make[4]: *** No rule to make target `../O.Common/osiFileName.h', needed by `inc'. Stop.

Took me a while to find out that the error was a missing config file.

EPICS is more helpful if the host architecture configuration is missing:

make EPICS_HOST_ARCH=nosuchhost
configure/CONFIG:54: configure/os/CONFIG.nosuchhost.Common: No such file or directory
make: *** No rule to make target `configure/os/CONFIG.nosuchhost.Common'. Stop.

Not nice but points in the correct direction.