Revert "Use compiler builtins for fabs."

Use of "extern inline" breaks clang build.

This reverts commit d76f16973a9d06765fb1f482239b9559f893ffd0.

Change-Id: I995d0d38c3776f5c50b060f16770741c92a2acac
diff --git a/libm/Android.mk b/libm/Android.mk
index 2d55b1d..7b28f70 100644
--- a/libm/Android.mk
+++ b/libm/Android.mk
@@ -108,6 +108,8 @@
     upstream-freebsd/lib/msun/src/s_exp2.c \
     upstream-freebsd/lib/msun/src/s_exp2f.c \
     upstream-freebsd/lib/msun/src/s_expm1f.c \
+    upstream-freebsd/lib/msun/src/s_fabs.c \
+    upstream-freebsd/lib/msun/src/s_fabsf.c \
     upstream-freebsd/lib/msun/src/s_fdim.c \
     upstream-freebsd/lib/msun/src/s_finite.c \
     upstream-freebsd/lib/msun/src/s_finitef.c \
@@ -173,6 +175,7 @@
     upstream-freebsd/lib/msun/src/s_copysignl.c \
     upstream-freebsd/lib/msun/src/e_coshl.c \
     upstream-freebsd/lib/msun/src/s_cosl.c \
+    upstream-freebsd/lib/msun/src/s_fabsl.c \
     upstream-freebsd/lib/msun/src/s_floorl.c \
     upstream-freebsd/lib/msun/src/s_fmal.c \
     upstream-freebsd/lib/msun/src/s_fmaxl.c \
@@ -225,10 +228,6 @@
 LOCAL_SRC_FILES += \
     signbit.c \
 
-# Home-grown stuff.
-LOCAL_SRC_FILES += \
-    fabs.cpp \
-
 # Arch specific optimizations.
 
 # -----------------------------------------------------------------------------