[libc] Fix incorrectly enabled GPU math functions (#83594)

Summary:
These functions were implemented via builtins that aren't acually
supported. See https://godbolt.org/z/Wq6q6T1za. This caused the build to
crash if they were included. Remove these and replace with correct
implementations.

Author: jhuber6

libc/src/math/amdgpu/CMakeLists.txt

@@ -176,46 +176,6 @@ add_entrypoint_object(
     -O2
 )
 
-add_entrypoint_object(
-  lround
-  SRCS
-    lround.cpp
-  HDRS
-    ../lround.h
-  COMPILE_OPTIONS
-    -O2
-)
-
-add_entrypoint_object(
-  lroundf
-  SRCS
-    lroundf.cpp
-  HDRS
-    ../lroundf.h
-  COMPILE_OPTIONS
-    -O2
-)
-
-add_entrypoint_object(
-  llround
-  SRCS
-    llround.cpp
-  HDRS
-    ../llround.h
-  COMPILE_OPTIONS
-    -O2
-)
-
-add_entrypoint_object(
-  llroundf
-  SRCS
-    llroundf.cpp
-  HDRS
-    ../llroundf.h
-  COMPILE_OPTIONS
-    -O2
-)
-
 add_entrypoint_object(
   modf
   SRCS

libc/src/math/amdgpu/exp.cpp

@@ -13,6 +13,6 @@
 
 namespace LIBC_NAMESPACE {
 
-LLVM_LIBC_FUNCTION(double, exp, (double x)) { return __builtin_exp(x); }
+LLVM_LIBC_FUNCTION(double, exp, (double x)) { return __ocml_exp_f64(x); }
 
 } // namespace LIBC_NAMESPACE

libc/src/math/amdgpu/expf.cpp

@@ -13,6 +13,6 @@
 
 namespace LIBC_NAMESPACE {
 
-LLVM_LIBC_FUNCTION(float, expf, (float x)) { return __builtin_expf(x); }
+LLVM_LIBC_FUNCTION(float, expf, (float x)) { return __ocml_exp_f32(x); }
 
 } // namespace LIBC_NAMESPACE

libc/src/math/amdgpu/llround.cpp

@@ -177,46 +177,6 @@ add_entrypoint_object(
     -O2
 )
 
-add_entrypoint_object(
-  lround
-  SRCS
-    lround.cpp
-  HDRS
-    ../lround.h
-  COMPILE_OPTIONS
-    -O2
-)
-
-add_entrypoint_object(
-  lroundf
-  SRCS
-    lroundf.cpp
-  HDRS
-    ../lroundf.h
-  COMPILE_OPTIONS
-    -O2
-)
-
-add_entrypoint_object(
-  llround
-  SRCS
-    llround.cpp
-  HDRS
-    ../llround.h
-  COMPILE_OPTIONS
-    -O2
-)
-
-add_entrypoint_object(
-  llroundf
-  SRCS
-    llroundf.cpp
-  HDRS
-    ../llroundf.h
-  COMPILE_OPTIONS
-    -O2
-)
-
 add_entrypoint_object(
   modf
   SRCS