giza: build fix for 10.7

* blacklist 10.7 Xcode clang, fix error: "invalid instruction mnemonic cvtsi2ssl"
* add openmaintainer

science/giza/Portfile

@@ -7,7 +7,9 @@ PortGroup github    1.0
 github.setup        danieljprice giza 1.5.0 v
 revision            0
 categories          science graphics fortran
-maintainers         {monash.edu:daniel.price @danieljprice}
+maintainers         {monash.edu:daniel.price @danieljprice} \
+                    openmaintainer
+
 description         C/Fortran graphics library, PGPLOT replacement
 long_description    giza is a 2D scientific plotting library \
                     for C/Fortran built on the cairo graphics library. \
@@ -31,6 +33,13 @@ depends_build       port:pkgconfig
 depends_lib         path:lib/pkgconfig/cairo.pc:cairo \
                     port:xorg-libX11
 
+# Xcode clang of 10.7 fails with error:
+# <stdin>:2579:2: error: invalid instruction mnemonic 'cvtsi2ssl' and others
+# https://github.com/william-dawson/NTPoly/issues/192
+# Note: This fixes same errors from gfortran, as well as clang.
+compiler.blacklist-append \
+                    {clang < 500}
+
 compilers.setup     require_fortran -g95
 
 configure.args      --disable-silent-rules