emulators/simh-hp3000: fix the build with LLVM 11.

Similar to the patch for emulators/simh-hp2100, drop an -fcommon in to fix
the build in the face of GCC 10 / LLVM 11 switching the default to
-fno-common.

Minor cleanup while we're here, remove USES= compiler and just use ${CC} for
the compiler.

PR:		248872
MFH:		2020Q3 (-fno-common build fix)

emulators/simh-hp3000/Makefile

@@ -22,7 +22,7 @@ LICENSE_PERMS=	dist-mirror dist-sell pkg-mirror pkg-sell auto-accept
 
 RUN_DEPENDS=	${LOCALBASE}/share/doc/hpdoc/simh_doc.pdf:emulators/simh-hpdoc
 
-USES=		compiler gmake dos2unix zip
+USES=		gmake dos2unix zip
 
 NO_WRKSUBDIR=	yes
 
@@ -34,7 +34,7 @@ SUB_FILES=	hp3000.1
 .include <bsd.port.pre.mk>
 
 do-build:
-	(cd ${WRKSRC}; GCC=${CHOSEN_COMPILER_TYPE} ${GMAKE} -C SCP hp3000)
+	(cd ${WRKSRC}; GCC=${CC} ${GMAKE} -C SCP hp3000)
 
 do-install:
 	${INSTALL_PROGRAM} ${WRKSRC}/hp3000 ${STAGEDIR}${PREFIX}/bin

emulators/simh-hp3000/files/patch-SCP_makefile

@@ -0,0 +1,17 @@
+--- SCP/makefile.orig	2020-08-23 21:58:56 UTC
++++ SCP/makefile
+@@ -532,10 +532,12 @@ ifneq ($(DONT_USE_READER_THREAD),)
+ endif
+ 
+ 
+-# Shut up annoying clang default warnings.
++# Shut up annoying clang default warnings, and also fix
++# multiply defined symbols on clang 11 and above
+ 
+-ifeq ($(GCC),clang)
++ifeq ($(findstring clang,$(COMPILER_NAME)),clang)
+   OS_CCDEFS += -Wno-parentheses -Wno-bitwise-op-parentheses -Wno-dangling-else
++  CFLAGS_O += -fcommon
+ endif
+ 
+