Fix newer GCC compiler warnings.

[cbalint13]

Proposed PR fixes the compiler warnings below.

• The offending lines were introduced by PR [Parser] Parser 2.0 part 2  #6162

• The fix is proposed in accord with discussions from here

[ 27%] Building CXX object CMakeFiles/tvm.dir/src/printer/text_printer.cc.o
/home/cbalint/work/TVM/tvm.marlann/src/parser/parser.cc: In member function ‘tvm::parser::Definitions tvm::parser::Parser::ParseDefinitions()’:
/home/cbalint/work/TVM/tvm.marlann/src/parser/parser.cc:667:38: warning: catching polymorphic type ‘struct tvm::parser::DuplicateKeyError’ by value [-Wcatch-value=]
  667 |           } catch (DuplicateKeyError e) {
      |                                      ^
/home/cbalint/work/TVM/tvm.marlann/src/parser/parser.cc: In member function ‘tvm::relay::TypeData tvm::parser::Parser::ParseTypeDef()’:
/home/cbalint/work/TVM/tvm.marlann/src/parser/parser.cc:706:32: warning: catching polymorphic type ‘struct tvm::parser::DuplicateKeyError’ by value [-Wcatch-value=]
  706 |     } catch (DuplicateKeyError e) {
      |                                ^
/home/cbalint/work/TVM/tvm.marlann/src/parser/parser.cc: In lambda function:
/home/cbalint/work/TVM/tvm.marlann/src/parser/parser.cc:750:40: warning: catching polymorphic type ‘struct tvm::parser::DuplicateKeyError’ by value [-Wcatch-value=]
  750 |             } catch (DuplicateKeyError e) {
      |                                        ^
[ 28%] Building CXX object CMakeFiles/tvm.dir/src/printer/tir_hybrid_printer.cc.o
/home/cbalint/work/TVM/tvm.marlann/src/parser/parser.cc: In member function ‘tvm::parser::Expr tvm::parser::Parser::GetOp(const string&, const tvm::parser::Token&)’:
/home/cbalint/work/TVM/tvm.marlann/src/parser/parser.cc:1344:26: warning: catching polymorphic type ‘struct dmlc::Error’ by value [-Wcatch-value=]
 1344 |     } catch (dmlc::Error e) {

Used GCC compiler:

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/10/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap --enable-languages=c,c++,fortran,objc,obj-c++,ada,go,d,lto --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-gcc-major-version-only --with-linker-hash-style=gnu --enable-plugin --enable-initfini-array --with-isl --enable-offload-targets=nvptx-none --without-cuda-driver --enable-gnu-indirect-function --enable-cet --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 10.2.1 20200804 (Red Hat 10.2.1-2) (GCC) 

@jroesch, please help with the review.

Thank You !

[tqchen]

Thanks @cbalint13 !