build: remove duplicate C++ standard flags from LIEF

LIEF's lief.gyp explicitly sets -std=gnu++17 in cflags_cc and
xcode_settings, while common.gypi already sets -std=gnu++20
project-wide. This results in both flags being passed to the compiler
(-std=gnu++20 -std=gnu++17). Since the last flag wins, LIEF was
silently compiling as C++17 instead of the intended project-wide C++20.

Remove the explicit -std=gnu++17 flags from cflags_cc and
xcode_settings.OTHER_CPLUSPLUSFLAGS, and the msvs_settings
LanguageStandard override (stdcpp17), so LIEF uses the project-wide
C++20 standard. LIEF is compatible with C++20 because
SPDLOG_USE_STD_FORMAT is not defined, so spdlog uses its bundled fmt
library rather than std::format, avoiding any C++20 conflicts.

Note: a separate issue with a stray debug string in the defines list
is addressed in a follow-up PR.

Fixes: #62129

Author: om-ghante

deps/LIEF/lief.gyp

@@ -454,14 +454,7 @@
       'cflags': [
         '-fPIC'
       ],
-      # We need c++17 to compile without std::format and avoid conflicts with spdlog.
-      'msvs_settings': {
-        'VCCLCompilerTool': {
-          'LanguageStandard': 'stdcpp17',
-        },
-      },
       'cflags_cc': [
-        '-std=gnu++17',
         '-fPIC',
         '-fvisibility=hidden',
         '-fvisibility-inlines-hidden',
@@ -474,7 +467,6 @@
       ],
       'xcode_settings': {
         'OTHER_CPLUSPLUSFLAGS': [
-          '-std=gnu++17',
           '-fPIC',
           '-fvisibility=hidden',
           '-fvisibility-inlines-hidden',