Be sensitive to the number of warnings-as-errors emitted by clang 5

The `fcheck-new` business is seen here:
```
18:36:11.785 [QUIET] [system.out] 	echo "GAMMA_PROG=gamma"; \
18:36:11.786 [QUIET] [system.out] 	echo "if [ -f gamma_g ]; then "; \
18:36:11.787 [QUIET] [system.out] 	echo "  GAMMA_PROG=gamma_g"; \
18:36:11.788 [QUIET] [system.out] 	echo "fi"; \
18:36:11.789 [QUIET] [system.out] 	echo ""; \
18:36:11.789 [ERROR] [system.err] clang: clang: error: error: argument unused during compilation: '-fcheck-new'argument unused during compilation: '-fcheck-new'
18:36:11.790 [QUIET] [system.out] 	echo "if [ \"Darwin\" = \"Darwin\" ]; then "; \
18:36:11.791 [ERROR] [system.err] 
18:36:11.791 [QUIET] [system.out] 	echo "  # Ensure architecture for gamma and JAVA_HOME is the same."; \
18:36:11.792 [ERROR] [system.err] clang: error: argument unused during compilation: '-fcheck-new'
18:36:11.793 [QUIET] [system.out] 	echo "  # NOTE: gamma assumes the OpenJDK directory layout."; \
18:36:11.793 [ERROR] [system.err] make[4]: *** [../generated/adfiles/archDesc.o] Error 1
```

The `COMPILER_WARNINGS_FATAL=false` is due to this:
```
18:33:19.033 [QUIET] [system.out] llvm-g++ -D_ALLBSD_SOURCE -D_GNU_SOURCE -DAMD64 -I/Volumes/seagate3/proj/DCEVM/src/share/vm/prims -I/Volumes/seagate3/proj/DCEVM/src/share/vm -I/Volumes/seagate3/proj/DCEVM/src/share/vm/precompiled -I/Volumes/seagate3/proj/DCEVM/src/cpu/x86/vm -I/Volumes/seagate3/proj/DCEVM/src/os_cpu/bsd_x86/vm -I/Volumes/seagate3/proj/DCEVM/src/os/bsd/vm -I/Volumes/seagate3/proj/DCEVM/src/os/posix/vm -I/Volumes/seagate3/proj/DCEVM/src/share/vm/adlc -I../generated -DASSERT -DTARGET_OS_FAMILY_bsd -DTARGET_ARCH_x86 -DTARGET_ARCH_MODEL_x86_64 -DTARGET_OS_ARCH_bsd_x86 -DTARGET_OS_ARCH_MODEL_bsd_x86_64 -DTARGET_COMPILER_gcc -DCOMPILER2 -DCOMPILER1  -fno-rtti -fno-exceptions -pthread -m64 -pipe -Werror -g -c -o ../generated/adfiles/dfa.o /Volumes/seagate3/proj/DCEVM/src/share/vm/adlc/dfa.cpp 
18:33:19.721 [ERROR] [system.err] /Volumes/seagate3/proj/DCEVM/src/share/vm/adlc/archDesc.cpp:335:35: error: '&&' within '||' [-Werror,-Wlogical-op-parentheses]
18:33:19.723 [ERROR] [system.err]     if ( instr->is_ideal_branch() && instr->label_position() == -1 ||
18:33:19.723 [ERROR] [system.err]          ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~
18:33:19.725 [ERROR] [system.err] /Volumes/seagate3/proj/DCEVM/src/share/vm/adlc/archDesc.cpp:335:35: note: place parentheses around the '&&' expression to silence this warning
18:33:19.725 [ERROR] [system.err]     if ( instr->is_ideal_branch() && instr->label_position() == -1 ||
18:33:19.725 [ERROR] [system.err]                                   ^
18:33:19.725 [ERROR] [system.err]          (                                                        )
18:33:19.726 [ERROR] [system.err] /Volumes/seagate3/proj/DCEVM/src/share/vm/adlc/archDesc.cpp:336:35: error: '&&' within '||' [-Werror,-Wlogical-op-parentheses]
18:33:19.726 [ERROR] [system.err]         !instr->is_ideal_branch() && instr->label_position() != -1) {
18:33:19.726 [ERROR] [system.err]         ~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
18:33:19.726 [ERROR] [system.err] /Volumes/seagate3/proj/DCEVM/src/share/vm/adlc/archDesc.cpp:336:35: note: place parentheses around the '&&' expression to silence this warning
18:33:19.726 [ERROR] [system.err]         !instr->is_ideal_branch() && instr->label_position() != -1) {
18:33:19.726 [ERROR] [system.err]                                   ^
18:33:19.727 [ERROR] [system.err]         (                                                         )
18:33:19.745 [ERROR] [system.err] 2 errors generated.
18:33:19.749 [ERROR] [system.err] make[4]: *** [../generated/adfiles/archDesc.o] Error 1
```