libm symbol cleanup.

Some of this code is used in the NDK libandroid_support now, as a static
library, so just being HIDDEN in the ELF sense isn't sufficient.

Rename digittoint to __libm_digittoint so we don't trample anyone's toes.

Also remove imprecise_powl and imprecise_tgammal. It turns out (to my
surprise) that we don't even have ld128 implementations of powl and tgammal,
so even LP64 was just using the "fake_long_double.c" hack in effect. Since
that's the case, let's *actually* do that because then we're not polluting
with the internal names in addition to the aliases.

Bug: N/A
Test: readelf
Change-Id: I273cc8fdc7ce53f9b8dfd4ef7796e358fe901837
diff --git a/libm/Android.bp b/libm/Android.bp
index 8947f4d..75e8957 100644
--- a/libm/Android.bp
+++ b/libm/Android.bp
@@ -63,7 +63,6 @@
         "upstream-freebsd/lib/msun/src/e_sinhf.c",
         "upstream-freebsd/lib/msun/src/e_sqrt.c",
         "upstream-freebsd/lib/msun/src/e_sqrtf.c",
-        "upstream-freebsd/lib/msun/src/imprecise.c",
         "upstream-freebsd/lib/msun/src/k_cos.c",
         "upstream-freebsd/lib/msun/src/k_cosf.c",
         "upstream-freebsd/lib/msun/src/k_exp.c",
@@ -209,6 +208,7 @@
         // Functionality not in the BSDs.
         "significandl.c",
         "sincos.c",
+        "fake_long_double.c",
 
         // Modified versions of BSD code.
         "signbit.c",
@@ -218,10 +218,6 @@
     ],
 
     multilib: {
-        lib32: {
-            srcs: ["fake_long_double.c"],
-        },
-
         lib64: {
             srcs: [
                 "upstream-freebsd/lib/msun/src/e_acosl.c",