cctools: try to use clang in as

The clang integrated assembler is way more up-to-date than the ancient
pre-GPLv3 version of gas that is the alternative. The latter doesn't
know about newer instructions such as AVX. The as(1) shipped with
recent Xcode versions will just run clang behind the scenes under most
circumstances for this reason.

Our cctools can't actually depend on clang because that would create a
circular dependency. So we'll try to run the clang corresponding to the
LLVM being used by cctools, and if that isn't present, try the system
clang in /usr/bin if we're on an OS version that has a clang with a
working integrated assembler. (The ancient gas is still used as a final
fallback.)

Fixes: https://trac.macports.org/ticket/37846

devel/cctools/Portfile

@@ -6,6 +6,7 @@ name                    cctools
 # Xcode 10.0
 version                 921
 set ld64_version        409.12
+revision                1
 categories              devel
 platforms               darwin
 maintainers             {jeremyhu @jeremyhu} openmaintainer
@@ -37,7 +38,7 @@ patchfiles              cctools-829-lto.patch \
                         PR-12400897.patch \
                         cctools-862-prunetrie.patch \
                         cctools-921-noavx512.patch \
-                        not-clang.patch
+                        as-try-clang.patch
 
 if {${os.major} < 11} {
     patchfiles-append snowleopard-strnlen.patch
@@ -139,8 +140,18 @@ post-patch {
             reinplace "s:\"llvm-objdump\":\"llvm-objdump-mp-${llvm_version}\":" ${worksrcpath}/otool/main.c
             reinplace "s:\"llvm-mc\":\"llvm-mc-mp-${llvm_version}\":" ${worksrcpath}/as/driver.c
             reinplace "s:@@LLVM_LIBDIR@@:${prefix}/libexec/llvm-${llvm_version}/lib:" ${worksrcpath}/libstuff/lto.c
+            reinplace "s:__MP_CLANG_NAME__:clang-mp-${llvm_version}:" ${worksrcpath}/as/driver.c
         }
 
+        if {${os.major} >= 11} {
+            set try_system_clang 1
+        } else {
+            # clang's integrated assembler may not work well on 10.6 and doesn't
+            # exist on older OS versions.
+            set try_system_clang 0
+        }
+        reinplace "s:__TRY_SYSTEM_CLANG__:${try_system_clang}:" ${worksrcpath}/as/driver.c
+
         foreach file [glob ${worksrcpath}/{*/,}Makefile] {
             reinplace "s:/usr/local:@PREFIX@:g" ${file}
             reinplace "s:/usr:@PREFIX@:g" ${file}

devel/cctools/files/as-try-clang.patch

@@ -0,0 +1,34 @@
+--- as/driver.c.orig	2018-09-19 08:01:56.000000000 +1000
++++ as/driver.c	2019-01-25 01:35:21.000000000 +1100
+@@ -295,11 +295,18 @@ char **envp)
+ 	    arch_flag.cputype == CPU_TYPE_ARM64 ||
+ 	    arch_flag.cputype == CPU_TYPE_ARM64_32 ||
+ 	    arch_flag.cputype == CPU_TYPE_ARM)){
+-	    as = makestr(prefix, CLANG, NULL);
+-	    if(access(as, F_OK) != 0){
+-		printf("%s: assembler (%s) not installed\n", progname, as);
+-		exit(1);
+-	    }
++        as = makestr(prefix, "__MP_CLANG_NAME__", NULL);
++        if(access(as, F_OK) != 0){
++#if __TRY_SYSTEM_CLANG__
++            as = "/usr/bin/clang";
++            if(access(as, F_OK) != 0){
++                as = NULL;
++            }
++#else
++            as = NULL;
++#endif
++        }
++        if (as != NULL) {
+ 	    new_argv = allocate((argc + 8) * sizeof(char *));
+ 	    new_argv[0] = as;
+ 	    j = 1;
+@@ -360,6 +367,7 @@ char **envp)
+ 		exit(0);
+ 	    else
+ 		exit(1);
++        } /* as != NULL */
+ 	}
+
+ 	/*