libgcc_s: export the IEEE-128 long double runtime on powerpc64le

On powerpc64le with IEEE-128 long double, the long-double compiler-runtime
helpers are the *kf* soft-float functions (built from the tf sources,
renamed via -D in lib/libcompiler_rt/Makefile.inc) plus the complex
multc3/__divtc3. They are compiled into libgcc_s.so by the powerpc64le
SRCF block, but were never added to Symbol.map, so they stayed local and
unexported.

Every other IEEE-128 architecture already exports its scalar long-double
runtime -- aarch64 and riscv list the tf helpers in GCC_4.6.0. powerpc64le
was simply missed.

Because the helpers are unexported, any clang-built shared library that uses
long double leaves them undefined (permitted in a DSO), and linking an
executable against that DSO then fails under lld's default
--no-allow-shlib-undefined. For example science/harminv fails to link its
binary against its own libharminv.so with undefined multc3/divtc3; at
-O0, mulkf3/addkf3/__subkf3/__unordkf2 appear as well.

Export the full runtime, gated on the PowerPC-specific LONG_DOUBLE_IEEE128
predefine so no other architecture is affected: complex multc3/divtc3 in
GCC_4.0.0 (beside the other complex mul*c3), and the 28 scalar *kf*
functions in GCC_7.0.0. Node placement follows glibc/gcc symbol-versioning
history.

Differential Revision:	https://reviews.freebsd.org/D58248

lib/libgcc_s/Symbol.map

@@ -161,6 +161,10 @@ GCC_4.0.0 {
 	__mulsc3;
 #if defined(__amd64__) || defined(__i386__)
 	__mulxc3;
+#endif
+#if defined(__LONG_DOUBLE_IEEE128__)
+	__divtc3;
+	__multc3;
 #endif
 	__powidf2;
 	__powisf2;
@@ -233,4 +237,34 @@ GCC_7.0.0 {
 #ifdef __i386__
 	__divmoddi4;
 #endif
+#if defined(__LONG_DOUBLE_IEEE128__)
+	__addkf3;
+	__subkf3;
+	__mulkf3;
+	__divkf3;
+	__eqkf2;
+	__gekf2;
+	__gtkf2;
+	__lekf2;
+	__ltkf2;
+	__nekf2;
+	__unordkf2;
+	__extendsfkf2;
+	__extenddfkf2;
+	__trunckfsf2;
+	__trunckfdf2;
+	__fixkfsi;
+	__fixkfdi;
+	__fixkfti;
+	__fixunskfsi;
+	__fixunskfdi;
+	__fixunskfti;
+	__floatsikf;
+	__floatdikf;
+	__floattikf;
+	__floatunsikf;
+	__floatundikf;
+	__floatuntikf;
+	__powikf2;
+#endif
 };