SNOW-1333462 update gcc version to 8.3 or above (#387)

README.rst

@@ -22,7 +22,7 @@ To build the Snowflake PHP PDO Driver, the following software must be installed:
 - On Windows: Visual Studio 2019
 - On Linux:
 
-  - gcc 5.2 or higher. **Note**: on certain OS (e.g. Centos 7) the preinstalled gcc/libstdc++ version is below the required minimum. For Centos 7, this is 4.8.5, which is below the requirement. Building and using the PHP PDO driver might be unsuccessful on such OS's until the prerequisite is fulfilled, i.e. libraries upgraded to at least the minimum version.
+  - gcc 8.3 or higher. **Note**: on certain OS (e.g. Centos 7) the preinstalled gcc/libstdc++ version is below the required minimum. For Centos 7, this is 4.8.5, which is below the requirement. Building and using the PHP PDO driver might be unsuccessful on such OS's until the prerequisite is fulfilled, i.e. libraries upgraded to at least the minimum version.
   - cmake 2.8 or higher
 
 - On macOS:

scripts/_init.sh

@@ -21,26 +21,8 @@ if [[ -z "$CMAKE" ]]; then
 fi
 
 if [[ -z "$GCC" || -z "$GXX" ]]; then
-    if [[ "$(which gcc49)" ]]; then
-        GCC="$(which gcc49)"
-        GXX="$(which g++49)"
-    elif [[ "$(which gcc-4.9)" ]]; then
-        GCC="$(which gcc-4.9)"
-        GXX="$(which g++-4.9)"
-    elif [[ "$(which gcc52)" ]]; then
-        GCC="$(which gcc52)"
-        GXX="$(which g++52)"
-    elif [[ "$(which gcc62)" ]]; then
-        GCC="$(which gcc62)"
-        GXX="$(which g++62)"
-    elif [[ "$(which gcc72)" ]]; then
-        GCC="$(which gcc72)"
-        GXX="$(which g++72)"
-    else
-        # Default to system
-        GCC="$(which gcc)"
-        GXX="$(which g++)"
-    fi
+    GCC="$(which gcc)"
+    GXX="$(which g++)"
 fi
 
 if [[ "$PLATFORM" == "darwin" ]]; then