With this patch CFLAGS and LDFLAGS are separated, so CFLAGS only used when compiling and LDFLAGS only used when linking.
This would silence many clang's warnings about unused arguments.

diff --git a/Makefile b/Makefile
index 8246b78..508878c 100644
--- a/Makefile
+++ b/Makefile
@@ -142,7 +142,7 @@ CC_CMD = $(CC) $(CFLAGS_ALL) -c -o $@ $<
 ifeq ($(ADD_CFI),yes)
 	AS_CMD = LC_ALL=C awk -f $(srcdir)/tools/add-cfi.common.awk -f $(srcdir)/tools/add-cfi.$(ARCH).awk $< | $(CC) $(CFLAGS_ALL) -x assembler -c -o $@ -
 else
-	AS_CMD = $(CC_CMD)
+	AS_CMD = $(CC) -c -o $@ $<
 endif
 
 obj/%.o: $(srcdir)/%.s
@@ -164,7 +164,7 @@ obj/%.lo: $(srcdir)/%.c $(GENH) $(IMPH)
 	$(CC_CMD)
 
 lib/libc.so: $(LOBJS) $(LDSO_OBJS)
-	$(CC) $(CFLAGS_ALL) $(LDFLAGS_ALL) -nostdlib -shared \
+	$(CC) $(LDFLAGS_ALL) -nostdlib -shared \
 	-Wl,-e,_dlstart -o $@ $(LOBJS) $(LDSO_OBJS) $(LIBCC)
 
 lib/libc.a: $(AOBJS)
diff --git a/configure b/configure
index c2db298..9f01ae5 100755
--- a/configure
+++ b/configure
@@ -39,6 +39,7 @@ Optional features:
 Some influential environment variables:
   CC                      C compiler command [detected]
   CFLAGS                  C compiler flags [-Os -pipe ...]
+  LDFLAGS                 linker flags [none]
   CROSS_COMPILE           prefix for cross compiler and tools [none]
   LIBCC                   compiler runtime library [detected]
 
@@ -337,9 +338,17 @@ tryflag CFLAGS_C99FSE -std=c99
 tryflag CFLAGS_C99FSE -nostdinc
 tryflag CFLAGS_C99FSE -ffreestanding \
 || tryflag CFLAGS_C99FSE -fno-builtin
+
+#
+# Do not check for excess-precision=standard and rounding-math on clang
+# because the test doesn't fail, but clang shows them as
+# unsupported optimization flags
+#
+if test "$cc_family" != clang ; then
 tryflag CFLAGS_C99FSE -fexcess-precision=standard \
 || { test "$ARCH" = i386 && tryflag CFLAGS_C99FSE -ffloat-store ; }
 tryflag CFLAGS_C99FSE -frounding-math
+fi
 
 #
 # We may use the may_alias attribute if __GNUC__ is defined, so