Clarify what --disable-asm does

Makefile.in

@@ -207,7 +207,9 @@ am__DIST_COMMON = $(srcdir)/Makefile.in \
 	$(top_srcdir)/src/libsodium/include/sodium/version.h.in \
 	AUTHORS ChangeLog THANKS build-aux/compile \
 	build-aux/config.guess build-aux/config.sub \
-	build-aux/install-sh build-aux/ltmain.sh build-aux/missing
+	build-aux/install-sh build-aux/ltmain.sh build-aux/missing \
+	compile config.guess config.sub depcomp install-sh ltmain.sh \
+	missing
 DISTFILES = $(DIST_COMMON) $(DIST_SOURCES) $(TEXINFOS) $(EXTRA_DIST)
 distdir = $(PACKAGE)-$(VERSION)
 top_distdir = $(distdir)

configure

@@ -1488,9 +1488,10 @@ Optional Features:
   --disable-dependency-tracking
                           speeds up one-time build
   --disable-ssp           Do not compile with -fstack-protector
-  --disable-asm           Do not compile assembly code -- This disables all
-                          (including non-assembly) platform-specific
-                          optimizations on Unix systems
+  --disable-asm           Do not compile assembly code -- As a side effect,
+                          this disables CPU-specific implementations on
+                          non-Windows platforms. Only for use with targets
+                          such as WebAssembly and NativeClient.
   --disable-pie           Do not produce position independent executables
   --enable-blocking-random
                           Enable this switch only if /dev/urandom is totally

configure.ac

@@ -61,7 +61,7 @@ AC_ARG_ENABLE(ssp,
 ])
 
 AC_ARG_ENABLE(asm,
-[AS_HELP_STRING(--disable-asm,Do not compile assembly code -- This disables all (including non-assembly) platform-specific optimizations on Unix systems)],
+[AS_HELP_STRING(--disable-asm,[Do not compile assembly code -- As a side effect, this disables CPU-specific implementations on non-Windows platforms. Only for use with targets such as WebAssembly and NativeClient.])],
 [
   AS_IF([test "x$enableval" = "xno"], [
     enable_asm="no"