toolchain/gcc: remove uclibc hack

This was introduced with 014d3b98b9 , which
is almost 10 years old. uClibc-ng does not suffer from this problem.

Note that this hack prevents libstdc++ from using C++11 math functions.

Tested by removing all of the mpd patches designed to fix this and
compiling.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

toolchain/gcc/common.mk

@@ -74,9 +74,6 @@ TAR_OPTIONS += \
 	--exclude=libjava
 
 export libgcc_cv_fixed_point=no
-ifdef CONFIG_USE_UCLIBC
-  export glibcxx_cv_c99_math_tr1=no
-endif
 ifdef CONFIG_INSTALL_GCCGO
   export libgo_cv_c_split_stack_supported=no
 endif