libjpeg-turbo: Support non-Altivec PowerPC

Closes: https://trac.macports.org/ticket/63259

graphics/libjpeg-turbo/Portfile

@@ -34,6 +34,7 @@ checksums           sha1    6bf63c869105d341011cd4915816de888338231a \
                     sha256  bef89803e506f27715c5627b1e3219c95b80fc31465d4452de2a909d382e4444 \
                     size    2255497
 
+configure.args      -DWITH_JPEG8=ON
 if {![info exists universal_possible]} {
     set universal_possible [expr {${os.universal_supported} && [llength ${configure.universal_archs}] >= 2}]
 }
@@ -46,8 +47,12 @@ if {${universal_possible} && [variant_isset universal]} {
 } elseif {${configure.build_arch} in {i386 x86_64}} {
     depends_build-append port:nasm
     configure.env       ASM_NASM=${prefix}/bin/nasm
+} elseif {${configure.build_arch} eq "ppc"} {
+    if {[catch {sysctl hw.vectorunit} result] || $result == 0} {
+        configure.args-append   -DWITH_SIMD=OFF
+        archive_sites
+    }
 }
-configure.args      -DWITH_JPEG8=1
 
 variant java description "Add Java support" {
     PortGroup           java 1.0