[libc] Add working entrypoints to riscv (#99885)

Added new fsqrt entrypoints and updated headers.txt, which I missed in PR #99771

Author: mikhailramalho

libc/config/linux/riscv/entrypoints.txt

@@ -449,6 +449,8 @@ set(TARGET_LIBM_ENTRYPOINTS
     libc.src.math.fromfpx
     libc.src.math.fromfpxf
     libc.src.math.fromfpxl
+    libc.src.math.fsqrt
+    libc.src.math.fsqrtl
     libc.src.math.hypot
     libc.src.math.hypotf
     libc.src.math.ilogb
@@ -575,6 +577,7 @@ if(LIBC_TYPES_HAS_FLOAT128)
     libc.src.math.frexpf128
     libc.src.math.fromfpf128
     libc.src.math.fromfpxf128
+    libc.src.math.fsqrtf128
     libc.src.math.ilogbf128
     libc.src.math.ldexpf128
     libc.src.math.llogbf128

libc/config/linux/riscv/headers.txt

@@ -2,6 +2,7 @@ set(TARGET_PUBLIC_HEADERS
     libc.include.assert
     libc.include.ctype
     libc.include.dirent
+    libc.include.dlfcn
     libc.include.errno
     libc.include.fcntl
     libc.include.features
@@ -18,6 +19,7 @@ set(TARGET_PUBLIC_HEADERS
     libc.include.setjmp
     libc.include.stdckdint
     libc.include.stdbit
+    libc.include.stdfix
     libc.include.stdio
     libc.include.stdlib
     libc.include.string
@@ -33,13 +35,12 @@ set(TARGET_PUBLIC_HEADERS
     libc.include.arpa_inet
 
     libc.include.sys_auxv
-    # Disabled due to epoll_wait syscalls not being available on this platform.
-    # libc.include.sys_epoll
+    libc.include.sys_epoll
     libc.include.sys_ioctl
     libc.include.sys_mman
     libc.include.sys_prctl
-    libc.include.sys_random
     libc.include.sys_queue
+    libc.include.sys_random
     libc.include.sys_resource
     libc.include.sys_select
     libc.include.sys_socket